diff --git a/app/assets/javascripts/discourse/helpers/application.js.es6 b/app/assets/javascripts/discourse/helpers/application.js.es6
index cac2ea1f0..02fa08fa8 100644
--- a/app/assets/javascripts/discourse/helpers/application.js.es6
+++ b/app/assets/javascripts/discourse/helpers/application.js.es6
@@ -9,12 +9,14 @@ Em.Handlebars.helper('bound-avatar', function(user, size, uploadId) {
     return new safe("<div class='avatar-placeholder'></div>");
   }
 
-  const username = Em.get(user, 'username');
+  const username = Em.get(user, 'username'),
+        letterAvatarColor = Em.get(user, 'letter_avatar_color');
+
   if (arguments.length < 4) { uploadId = Em.get(user, 'uploaded_avatar_id'); }
-  const avatar = Em.get(user, 'avatar_template') || avatarTemplate(username, uploadId);
+  const avatar = Em.get(user, 'avatar_template') || avatarTemplate(username, uploadId, letterAvatarColor);
 
   return new safe(Discourse.Utilities.avatarImg({ size: size, avatarTemplate: avatar }));
-}, 'username', 'uploaded_avatar_id', 'avatar_template');
+}, 'username', 'uploaded_avatar_id', 'letter_avatar_color', 'avatar_template');
 
 /*
  * Used when we only have a template
diff --git a/app/assets/javascripts/discourse/helpers/user-avatar.js.es6 b/app/assets/javascripts/discourse/helpers/user-avatar.js.es6
index 1ab668ffc..aea2e9baa 100644
--- a/app/assets/javascripts/discourse/helpers/user-avatar.js.es6
+++ b/app/assets/javascripts/discourse/helpers/user-avatar.js.es6
@@ -5,20 +5,20 @@ function renderAvatar(user, options) {
   options = options || {};
 
   if (user) {
-    var username = Em.get(user, 'username');
+    let username = Em.get(user, 'username');
     if (!username) {
       if (!options.usernamePath) { return ''; }
       username = Em.get(user, options.usernamePath);
     }
 
-    var title;
+    let title;
     if (!options.ignoreTitle) {
       // first try to get a title
       title = Em.get(user, 'title');
       // if there was no title provided
       if (!title) {
         // try to retrieve a description
-        var description = Em.get(user, 'description');
+        const description = Em.get(user, 'description');
         // if a description has been provided
         if (description && description.length > 0) {
           // preprend the username before the description
@@ -28,13 +28,14 @@ function renderAvatar(user, options) {
     }
 
     // this is simply done to ensure we cache images correctly
-    var uploadedAvatarId = Em.get(user, 'uploaded_avatar_id') || Em.get(user, 'user.uploaded_avatar_id');
+    const uploadedAvatarId = Em.get(user, 'uploaded_avatar_id') || Em.get(user, 'user.uploaded_avatar_id'),
+          letterAvatarColor = Em.get(user, 'letter_avatar_color') || Em.get(user, 'user.letter_avatar_color');
 
     return Discourse.Utilities.avatarImg({
       size: options.imageSize,
       extraClasses: Em.get(user, 'extras') || options.extraClasses,
       title: title || username,
-      avatarTemplate: avatarTemplate(username, uploadedAvatarId)
+      avatarTemplate: Em.get("avatar_template") || avatarTemplate(username, uploadedAvatarId, letterAvatarColor)
     });
   } else {
     return '';
diff --git a/app/assets/javascripts/discourse/lib/avatar-template.js.es6 b/app/assets/javascripts/discourse/lib/avatar-template.js.es6
index 542e97959..731a2047d 100644
--- a/app/assets/javascripts/discourse/lib/avatar-template.js.es6
+++ b/app/assets/javascripts/discourse/lib/avatar-template.js.es6
@@ -2,8 +2,10 @@ import { hashString } from 'discourse/lib/hash';
 
 let _splitAvatars;
 
-function defaultAvatar(username) {
-  const defaultAvatars = Discourse.SiteSettings.default_avatars;
+function defaultAvatar(username, letterAvatarColor) {
+  const defaultAvatars = Discourse.SiteSettings.default_avatars,
+        version = Discourse.LetterAvatarVersion;
+
   if (defaultAvatars && defaultAvatars.length) {
     _splitAvatars = _splitAvatars || defaultAvatars.split("\n");
 
@@ -13,20 +15,17 @@ function defaultAvatar(username) {
     }
   }
 
-  return Discourse.getURLWithCDN("/letter_avatar/" +
-                                 username.toLowerCase() +
-                                 "/{size}/" +
-                                 Discourse.LetterAvatarVersion + ".png");
+  if (Discourse.SiteSettings.external_letter_avatars_enabled) {
+    const url = Discourse.SiteSettings.external_letter_avatars_url;
+    return `${url}/letter/${username[0]}?color=${letterAvatarColor}&size={size}`;
+  } else {
+    return Discourse.getURLWithCDN(`/letter_avatar/${username.toLowerCase()}/{size}/${version}.png`);
+  }
 }
 
-export default function(username, uploadedAvatarId) {
+export default function(username, uploadedAvatarId, letterAvatarColor) {
   if (uploadedAvatarId) {
-    return Discourse.getURLWithCDN("/user_avatar/" +
-                                   Discourse.BaseUrl +
-                                   "/" +
-                                   username.toLowerCase() +
-                                   "/{size}/" +
-                                   uploadedAvatarId + ".png");
+    return Discourse.getURLWithCDN(`/user_avatar/${Discourse.BaseUrl}/${username.toLowerCase()}/{size}/${uploadedAvatarId}.png`);
   }
-  return defaultAvatar(username);
+  return defaultAvatar(username, letterAvatarColor);
 }
diff --git a/app/assets/javascripts/discourse/models/user-action.js.es6 b/app/assets/javascripts/discourse/models/user-action.js.es6
index 2d273c43e..05e1e4929 100644
--- a/app/assets/javascripts/discourse/models/user-action.js.es6
+++ b/app/assets/javascripts/discourse/models/user-action.js.es6
@@ -1,5 +1,7 @@
 import RestModel from 'discourse/models/rest';
 import { url } from 'discourse/lib/computed';
+import { on } from 'ember-addons/ember-computed-decorators';
+import computed from 'ember-addons/ember-computed-decorators';
 
 const UserActionTypes = {
   likes_given: 1,
@@ -17,21 +19,22 @@ const UserActionTypes = {
 };
 const InvertedActionTypes = {};
 
-_.each(UserActionTypes, function (k, v) {
+_.each(UserActionTypes, (k, v) => {
   InvertedActionTypes[k] = v;
 });
 
 const UserAction = RestModel.extend({
 
-  _attachCategory: function() {
+  @on("init")
+  _attachCategory() {
     const categoryId = this.get('category_id');
     if (categoryId) {
       this.set('category', Discourse.Category.findById(categoryId));
     }
-  }.on('init'),
+  },
 
-  descriptionKey: function() {
-    const action = this.get('action_type');
+  @computed("action_type")
+  descriptionKey(action) {
     if (action === null || Discourse.UserAction.TO_SHOW.indexOf(action) >= 0) {
       if (this.get('isPM')) {
         return this.get('sameUser') ? 'sent_by_you' : 'sent_by_user';
@@ -59,34 +62,39 @@ const UserAction = RestModel.extend({
         return this.get('targetUser') ? 'user_mentioned_you' : 'user_mentioned_user';
       }
     }
-  }.property('action_type'),
+  },
 
-  sameUser: function() {
-    return this.get('username') === Discourse.User.currentProp('username');
-  }.property('username'),
+  @computed("username")
+  sameUser(username) {
+    return username === Discourse.User.currentProp('username');
+  },
 
-  targetUser: function() {
-    return this.get('target_username') === Discourse.User.currentProp('username');
-  }.property('target_username'),
+  @computed("target_username")
+  targetUser(targetUsername) {
+    return targetUsername === Discourse.User.currentProp('username');
+  },
 
   presentName: Em.computed.any('name', 'username'),
   targetDisplayName: Em.computed.any('target_name', 'target_username'),
   actingDisplayName: Em.computed.any('acting_name', 'acting_username'),
   targetUserUrl: url('target_username', '/users/%@'),
 
-  usernameLower: function() {
-    return this.get('username').toLowerCase();
-  }.property('username'),
+  @computed("username")
+  usernameLower(username) {
+    return username.toLowerCase();
+  },
 
   userUrl: url('usernameLower', '/users/%@'),
 
-  postUrl: function() {
+  @computed()
+  postUrl() {
     return Discourse.Utilities.postUrl(this.get('slug'), this.get('topic_id'), this.get('post_number'));
-  }.property(),
+  },
 
-  replyUrl: function() {
+  @computed()
+  replyUrl() {
     return Discourse.Utilities.postUrl(this.get('slug'), this.get('topic_id'), this.get('reply_to_post_number'));
-  }.property(),
+  },
 
   replyType: Em.computed.equal('action_type', UserActionTypes.replies),
   postType: Em.computed.equal('action_type', UserActionTypes.posts),
@@ -99,7 +107,7 @@ const UserAction = RestModel.extend({
   postReplyType: Em.computed.or('postType', 'replyType'),
   removableBookmark: Em.computed.and('bookmarkType', 'sameUser'),
 
-  addChild: function(action) {
+  addChild(action) {
     let groups = this.get("childGroups");
     if (!groups) {
       groups = {
@@ -143,22 +151,23 @@ const UserAction = RestModel.extend({
     "childGroups.edits.items", "childGroups.edits.items.@each",
     "childGroups.bookmarks.items", "childGroups.bookmarks.items.@each"),
 
-  switchToActing: function() {
+  switchToActing() {
     this.setProperties({
       username: this.get('acting_username'),
       uploaded_avatar_id: this.get('acting_uploaded_avatar_id'),
+      letter_avatar_color: this.get('action_letter_avatar_color'),
       name: this.get('actingDisplayName')
     });
   }
 });
 
 UserAction.reopenClass({
-  collapseStream: function(stream) {
+  collapseStream(stream) {
     const uniq = {};
     const collapsed = [];
     let pos = 0;
 
-    stream.forEach(function(item) {
+    stream.forEach(item => {
       const key = "" + item.topic_id + "-" + item.post_number;
       const found = uniq[key];
       if (found === void 0) {
diff --git a/app/assets/javascripts/discourse/models/user.js.es6 b/app/assets/javascripts/discourse/models/user.js.es6
index 01aef870a..8fac2812e 100644
--- a/app/assets/javascripts/discourse/models/user.js.es6
+++ b/app/assets/javascripts/discourse/models/user.js.es6
@@ -6,6 +6,7 @@ import UserPostsStream from 'discourse/models/user-posts-stream';
 import Singleton from 'discourse/mixins/singleton';
 import { longDate } from 'discourse/lib/formatter';
 import computed from 'ember-addons/ember-computed-decorators';
+import { observes } from 'ember-addons/ember-computed-decorators';
 import Badge from 'discourse/models/badge';
 import UserBadge from 'discourse/models/user-badge';
 
@@ -18,13 +19,15 @@ const User = RestModel.extend({
   hasNotPosted: Em.computed.not("hasPosted"),
   canBeDeleted: Em.computed.and("can_be_deleted", "hasNotPosted"),
 
-  stream: function() {
+  @computed()
+  stream() {
     return UserStream.create({ user: this });
-  }.property(),
+  },
 
-  postsStream: function() {
+  @computed()
+  postsStream() {
     return UserPostsStream.create({ user: this });
-  }.property(),
+  },
 
   staff: Em.computed.or('admin', 'moderator'),
 
@@ -32,27 +35,22 @@ const User = RestModel.extend({
     return Discourse.ajax(`/session/${this.get('username')}`, { type: 'DELETE'});
   },
 
-  searchContext: function() {
+  @computed("username_lower")
+  searchContext(username) {
     return {
       type: 'user',
-      id: this.get('username_lower'),
+      id: username,
       user: this
     };
-  }.property('username_lower'),
+  },
 
-  /**
-    This user's display name. Returns the name if possible, otherwise returns the
-    username.
-
-    @property displayName
-    @type {String}
-  **/
-  displayName: function() {
-    if (Discourse.SiteSettings.enable_names && !Ember.isEmpty(this.get('name'))) {
-      return this.get('name');
+  @computed("username", "name")
+  displayName(username, name) {
+    if (Discourse.SiteSettings.enable_names && !Ember.isEmpty(name)) {
+      return name;
     }
-    return this.get('username');
-  }.property('username', 'name'),
+    return username;
+  },
 
   @computed('profile_background')
   profileBackground(bgUrl) {
@@ -60,38 +58,23 @@ const User = RestModel.extend({
     return ('background-image: url(' + Discourse.getURLWithCDN(bgUrl) + ')').htmlSafe();
   },
 
-  path: function(){
-    return Discourse.getURL('/users/' + this.get('username_lower'));
+  @computed()
+  path() {
     // no need to observe, requires a hard refresh to update
-  }.property(),
+    return Discourse.getURL(`/users/${this.get('username_lower')}`);
+  },
 
-  /**
-    Path to this user's administration
-
-    @property adminPath
-    @type {String}
-  **/
   adminPath: url('username_lower', "/admin/users/%@"),
 
-  /**
-    This user's username in lowercase.
+  @computed("username")
+  username_lower(username) {
+    return username.toLowerCase();
+  },
 
-    @property username_lower
-    @type {String}
-  **/
-  username_lower: function() {
-    return this.get('username').toLowerCase();
-  }.property('username'),
-
-  /**
-    This user's trust level.
-
-    @property trustLevel
-    @type {Integer}
-  **/
-  trustLevel: function() {
-    return Discourse.Site.currentProp('trustLevels').findProperty('id', parseInt(this.get('trust_level'), 10));
-  }.property('trust_level'),
+  @computed("trust_level")
+  trustLevel(trustLevel) {
+    return Discourse.Site.currentProp('trustLevels').findProperty('id', parseInt(trustLevel, 10));
+  },
 
   isBasic: Em.computed.equal('trust_level', 0),
   isLeader: Em.computed.equal('trust_level', 3),
@@ -100,61 +83,36 @@ const User = RestModel.extend({
 
   isSuspended: Em.computed.equal('suspended', true),
 
-  suspended: function() {
-    return this.get('suspended_till') && moment(this.get('suspended_till')).isAfter();
-  }.property('suspended_till'),
+  @computed("suspended_till")
+  suspended(suspendedTill) {
+    return suspendedTill && moment(suspendedTill).isAfter();
+  },
 
-  suspendedTillDate: function() {
-    return longDate(this.get('suspended_till'));
-  }.property('suspended_till'),
+  @computed("suspended_till")
+  suspendedTillDate(suspendedTill) {
+    return longDate(suspendedTill);
+  },
 
-  /**
-    Changes this user's username.
-
-    @method changeUsername
-    @param {String} newUsername The user's new username
-    @returns Result of ajax call
-  **/
-  changeUsername: function(newUsername) {
-    return Discourse.ajax("/users/" + this.get('username_lower') + "/preferences/username", {
+  changeUsername(new_username) {
+    return Discourse.ajax(`/users/${this.get('username_lower')}/preferences/username`, {
       type: 'PUT',
-      data: { new_username: newUsername }
+      data: { new_username }
     });
   },
 
-  /**
-    Changes this user's email address.
-
-    @method changeEmail
-    @param {String} email The user's new email address\
-    @returns Result of ajax call
-  **/
-  changeEmail: function(email) {
-    return Discourse.ajax("/users/" + this.get('username_lower') + "/preferences/email", {
+  changeEmail(email) {
+    return Discourse.ajax(`/users/${this.get('username_lower')}/preferences/email`, {
       type: 'PUT',
-      data: { email: email }
+      data: { email }
     });
   },
 
-  /**
-    Returns a copy of this user.
-
-    @method copy
-    @returns {User}
-  **/
-  copy: function() {
+  copy() {
     return Discourse.User.create(this.getProperties(Ember.keys(this)));
   },
 
-  /**
-    Save's this user's properties over AJAX via a PUT request.
-
-    @method save
-    @returns {Promise} the result of the operation
-  **/
-  save: function() {
-    const self = this,
-          data = this.getProperties(
+  save() {
+    const data = this.getProperties(
             'auto_track_topics_after_msecs',
             'bio_raw',
             'website',
@@ -179,10 +137,10 @@ const User = RestModel.extend({
             'card_background'
           );
 
-    ['muted','watched','tracked'].forEach(function(s){
-      var cats = self.get(s + 'Categories').map(function(c){ return c.get('id')});
+    ['muted','watched','tracked'].forEach(s => {
+      let cats = this.get(s + 'Categories').map(c => c.get('id'));
       // HACK: denote lack of categories
-      if(cats.length === 0) { cats = [-1]; }
+      if (cats.length === 0) { cats = [-1]; }
       data[s + '_category_ids'] = cats;
     });
 
@@ -192,26 +150,19 @@ const User = RestModel.extend({
 
     // TODO: We can remove this when migrated fully to rest model.
     this.set('isSaving', true);
-    return Discourse.ajax("/users/" + this.get('username_lower'), {
+    return Discourse.ajax(`/users/${this.get('username_lower')}`, {
       data: data,
       type: 'PUT'
-    }).then(function(result) {
-      self.set('bio_excerpt', result.user.bio_excerpt);
-
-      const userProps = self.getProperties('enable_quoting', 'external_links_in_new_tab', 'dynamic_favicon');
+    }).then(result => {
+      this.set('bio_excerpt', result.user.bio_excerpt);
+      const userProps = this.getProperties('enable_quoting', 'external_links_in_new_tab', 'dynamic_favicon');
       Discourse.User.current().setProperties(userProps);
     }).finally(() => {
       this.set('isSaving', false);
     });
   },
 
-  /**
-    Changes the password and calls the callback function on AJAX.complete.
-
-    @method changePassword
-    @returns {Promise} the result of the change password operation
-  **/
-  changePassword: function() {
+  changePassword() {
     return Discourse.ajax("/session/forgot_password", {
       dataType: 'json',
       data: { login: this.get('username') },
@@ -219,73 +170,63 @@ const User = RestModel.extend({
     });
   },
 
-  /**
-    Loads a single user action by id.
-
-    @method loadUserAction
-    @param {Integer} id The id of the user action being loaded
-    @returns A stream of the user's actions containing the action of id
-  **/
-  loadUserAction: function(id) {
-    var self = this,
-        stream = this.get('stream');
-    return Discourse.ajax("/user_actions/" + id + ".json", { cache: 'false' }).then(function(result) {
+  loadUserAction(id) {
+    const stream = this.get('stream');
+    return Discourse.ajax(`/user_actions/${id}.json`, { cache: 'false' }).then(result => {
       if (result && result.user_action) {
-        var ua = result.user_action;
+        const ua = result.user_action;
 
-        if ((self.get('stream.filter') || ua.action_type) !== ua.action_type) return;
-        if (!self.get('stream.filter') && !self.inAllStream(ua)) return;
+        if ((this.get('stream.filter') || ua.action_type) !== ua.action_type) return;
+        if (!this.get('stream.filter') && !this.inAllStream(ua)) return;
 
-        var action = Discourse.UserAction.collapseStream([Discourse.UserAction.create(ua)]);
+        const action = Discourse.UserAction.collapseStream([Discourse.UserAction.create(ua)]);
         stream.set('itemsLoaded', stream.get('itemsLoaded') + 1);
         stream.get('content').insertAt(0, action[0]);
       }
     });
   },
 
-  inAllStream: function(ua) {
+  inAllStream(ua) {
     return ua.action_type === Discourse.UserAction.TYPES.posts ||
            ua.action_type === Discourse.UserAction.TYPES.topics;
   },
 
   // The user's stat count, excluding PMs.
-  statsCountNonPM: function() {
-    var self = this;
-
+  @computed("statsExcludingPms.@each.count")
+  statsCountNonPM() {
     if (Ember.isEmpty(this.get('statsExcludingPms'))) return 0;
-    var count = 0;
-    _.each(this.get('statsExcludingPms'), function(val) {
-      if (self.inAllStream(val)){
+    let count = 0;
+    _.each(this.get('statsExcludingPms'), val => {
+      if (this.inAllStream(val)) {
         count += val.count;
       }
     });
     return count;
-  }.property('statsExcludingPms.@each.count'),
+  },
 
   // The user's stats, excluding PMs.
-  statsExcludingPms: function() {
+  @computed("stats.@each.isPM")
+  statsExcludingPms() {
     if (Ember.isEmpty(this.get('stats'))) return [];
     return this.get('stats').rejectProperty('isPM');
-  }.property('stats.@each.isPM'),
+  },
 
-  findDetails: function(options) {
-    var user = this;
+  findDetails(options) {
+    const user = this;
 
-    return PreloadStore.getAndRemove("user_" + user.get('username'), function() {
-      return Discourse.ajax("/users/" + user.get('username') + '.json', {data: options});
-    }).then(function (json) {
+    return PreloadStore.getAndRemove(`user_${user.get('username')}`, () => {
+      return Discourse.ajax(`/users/${user.get('username')}.json`, { data: options });
+    }).then(json => {
 
       if (!Em.isEmpty(json.user.stats)) {
-        json.user.stats = Discourse.User.groupStats(_.map(json.user.stats,function(s) {
+        json.user.stats = Discourse.User.groupStats(_.map(json.user.stats, s => {
           if (s.count) s.count = parseInt(s.count, 10);
           return Discourse.UserActionStat.create(s);
         }));
       }
 
       if (!Em.isEmpty(json.user.custom_groups)) {
-        json.user.custom_groups = json.user.custom_groups.map(function (g) {
-          return Discourse.Group.create(g);
-        });
+        json.user.custom_groups = json.user.custom_groups.map(g => Discourse.Group.create(g));
       }
 
       if (json.user.invited_by) {
@@ -294,12 +235,10 @@ const User = RestModel.extend({
 
       if (!Em.isEmpty(json.user.featured_user_badge_ids)) {
         const userBadgesMap = {};
-        UserBadge.createFromJson(json).forEach(function(userBadge) {
+        UserBadge.createFromJson(json).forEach(userBadge => {
           userBadgesMap[ userBadge.get('id') ] = userBadge;
         });
-        json.user.featured_user_badges = json.user.featured_user_badge_ids.map(function(id) {
-          return userBadgesMap[id];
-        });
+        json.user.featured_user_badges = json.user.featured_user_badge_ids.map(id => userBadgesMap[id]);
       }
 
       if (json.user.card_badge) {
@@ -311,30 +250,26 @@ const User = RestModel.extend({
     });
   },
 
-  findStaffInfo: function() {
+  findStaffInfo() {
     if (!Discourse.User.currentProp("staff")) { return Ember.RSVP.resolve(null); }
-    var self = this;
-    return Discourse.ajax("/users/" + this.get("username_lower") + "/staff-info.json").then(function(info) {
-      self.setProperties(info);
+    return Discourse.ajax(`/users/${this.get("username_lower")}/staff-info.json`).then(info => {
+      this.setProperties(info);
     });
   },
 
-  avatarTemplate: function() {
-    return avatarTemplate(this.get('username'), this.get('uploaded_avatar_id'));
-  }.property('uploaded_avatar_id', 'username'),
+  @computed("username", "uploaded_avatar_id", "letter_avatar_color")
+  avatarTemplate(username, uploadedAvatarId, letterAvatarColor) {
+    return avatarTemplate(username, uploadedAvatarId, letterAvatarColor);
+  },
 
   /*
     Change avatar selection
   */
-  pickAvatar: function(uploadId) {
-    var self = this;
-
-    return Discourse.ajax("/users/" + this.get("username_lower") + "/preferences/avatar/pick", {
+  pickAvatar(uploadId) {
+    return Discourse.ajax(`/users/${this.get("username_lower")}/preferences/avatar/pick`, {
       type: 'PUT',
       data: { upload_id: uploadId }
-    }).then(function(){
-      self.set('uploaded_avatar_id', uploadId);
-    });
+    }).then(() => this.set('uploaded_avatar_id', uploadId));
   },
 
   /**
@@ -344,7 +279,7 @@ const User = RestModel.extend({
     @param {String} type The type of the upload (image, attachment)
     @returns true if the current user is allowed to upload a file
   **/
-  isAllowedToUploadAFile: function(type) {
+  isAllowedToUploadAFile(type) {
     return this.get('staff') ||
            this.get('trust_level') > 0 ||
            Discourse.SiteSettings['newuser_max_' + type + 's'] > 0;
@@ -357,35 +292,39 @@ const User = RestModel.extend({
     @param {String} email The email address of the user to invite to the site
     @returns {Promise} the result of the server call
   **/
-  createInvite: function(email, groupNames) {
+  createInvite(email, groupNames) {
     return Discourse.ajax('/invites', {
       type: 'POST',
       data: {email: email, group_names: groupNames}
     });
   },
 
-  generateInviteLink: function(email, groupNames, topicId) {
+  generateInviteLink(email, groupNames, topicId) {
     return Discourse.ajax('/invites/link', {
       type: 'POST',
       data: {email: email, group_names: groupNames, topic_id: topicId}
     });
   },
 
-  updateMutedCategories: function() {
+  @observes("muted_category_ids")
+  updateMutedCategories() {
     this.set("mutedCategories", Discourse.Category.findByIds(this.muted_category_ids));
-  }.observes("muted_category_ids"),
+  },
 
-  updateTrackedCategories: function() {
+  @observes("tracked_category_ids")
+  updateTrackedCategories() {
     this.set("trackedCategories", Discourse.Category.findByIds(this.tracked_category_ids));
-  }.observes("tracked_category_ids"),
+  },
 
-  updateWatchedCategories: function() {
+  @observes("watched_category_ids")
+  updateWatchedCategories() {
     this.set("watchedCategories", Discourse.Category.findByIds(this.watched_category_ids));
-  }.observes("watched_category_ids"),
+  },
 
-  canDeleteAccount: function() {
-    return !Discourse.SiteSettings.enable_sso && this.get('can_delete_account') && ((this.get('reply_count')||0) + (this.get('topic_count')||0)) <= 1;
-  }.property('can_delete_account', 'reply_count', 'topic_count'),
+  @computed("can_delete_account", "reply_count", "topic_count")
+  canDeleteAccount(canDeleteAccount, replyCount, topicCount) {
+    return !Discourse.SiteSettings.enable_sso && canDeleteAccount && ((replyCount || 0) + (topicCount || 0)) <= 1;
+  },
 
   "delete": function() {
     if (this.get('can_delete_account')) {
@@ -398,27 +337,26 @@ const User = RestModel.extend({
     }
   },
 
-  dismissBanner: function (bannerKey) {
+  dismissBanner(bannerKey) {
     this.set("dismissed_banner_key", bannerKey);
-    Discourse.ajax("/users/" + this.get('username'), {
+    Discourse.ajax(`/users/${this.get('username')}`, {
       type: 'PUT',
       data: { dismissed_banner_key: bannerKey }
     });
   },
 
-  checkEmail: function () {
-    var self = this;
-    return Discourse.ajax("/users/" + this.get("username_lower") + "/emails.json", {
+  checkEmail() {
+    return Discourse.ajax(`/users/${this.get("username_lower")}/emails.json`, {
       type: "PUT",
       data: { context: window.location.pathname }
-    }).then(function (result) {
+    }).then(result => {
       if (result) {
-        self.setProperties({
+        this.setProperties({
           email: result.email,
           associated_accounts: result.associated_accounts
         });
       }
-    }, function () {});
+    });
   }
 
 });
@@ -426,14 +364,14 @@ const User = RestModel.extend({
 User.reopenClass(Singleton, {
 
   // Find a `Discourse.User` for a given username.
-  findByUsername: function(username, options) {
+  findByUsername(username, options) {
     const user = User.create({username: username});
     return user.findDetails(options);
   },
 
   // TODO: Use app.register and junk Singleton
-  createCurrent: function() {
-    var userJson = PreloadStore.get('currentUser');
+  createCurrent() {
+    const userJson = PreloadStore.get('currentUser');
     if (userJson) {
       const store = Discourse.__container__.lookup('store:main');
       return store.createRecord('user', userJson);
@@ -441,56 +379,38 @@ User.reopenClass(Singleton, {
     return null;
   },
 
-  /**
-    Checks if given username is valid for this email address
-
-    @method checkUsername
-    @param {String} username A username to check
-    @param {String} email An email address to check
-    @param {Number} forUserId user id - provide when changing username
-  **/
-  checkUsername: function(username, email, forUserId) {
+  checkUsername(username, email, for_user_id) {
     return Discourse.ajax('/users/check_username', {
-      data: { username: username, email: email, for_user_id: forUserId }
+      data: { username, email, for_user_id }
     });
   },
 
-  /**
-    Groups the user's statistics
-
-    @method groupStats
-    @param {Array} stats Given stats
-    @returns {Object}
-  **/
-  groupStats: function(stats) {
-    var responses = Discourse.UserActionStat.create({
+  groupStats(stats) {
+    const responses = Discourse.UserActionStat.create({
       count: 0,
       action_type: Discourse.UserAction.TYPES.replies
     });
 
-    stats.filterProperty('isResponse').forEach(function (stat) {
+    stats.filterProperty('isResponse').forEach(stat => {
       responses.set('count', responses.get('count') + stat.get('count'));
     });
 
-    var result = Em.A();
+    const result = Em.A();
     result.pushObjects(stats.rejectProperty('isResponse'));
 
-    var insertAt = 0;
-    result.forEach(function(item, index){
-     if(item.action_type === Discourse.UserAction.TYPES.topics || item.action_type === Discourse.UserAction.TYPES.posts){
+    let insertAt = 0;
+    result.forEach((item, index) => {
+     if (item.action_type === Discourse.UserAction.TYPES.topics || item.action_type === Discourse.UserAction.TYPES.posts) {
        insertAt = index + 1;
      }
     });
-    if(responses.count > 0) {
+    if (responses.count > 0) {
       result.insertAt(insertAt, responses);
     }
-    return(result);
+    return result;
   },
 
-  /**
-    Creates a new account
-  **/
-  createAccount: function(attrs) {
+  createAccount(attrs) {
     return Discourse.ajax("/users", {
       data: {
         name: attrs.accountName,
diff --git a/app/assets/javascripts/discourse/views/composer.js.es6 b/app/assets/javascripts/discourse/views/composer.js.es6
index d96c6a55a..6964d102a 100644
--- a/app/assets/javascripts/discourse/views/composer.js.es6
+++ b/app/assets/javascripts/discourse/views/composer.js.es6
@@ -252,9 +252,12 @@ const ComposerView = Ember.View.extend(Ember.Evented, {
           const quotedPost = posts.findProperty("post_number", postNumber);
           if (quotedPost) {
             const username = quotedPost.get('username'),
-                  uploadId = quotedPost.get('uploaded_avatar_id');
+                  uploadId = quotedPost.get('uploaded_avatar_id'),
+                  letterAvatarColor = quotedPost.get("letter_avatar_color");
 
-            return Discourse.Utilities.tinyAvatar(avatarTemplate(username, uploadId));
+            debugger;
+
+            return Discourse.Utilities.tinyAvatar(avatarTemplate(username, uploadId, letterAvatarColor));
           }
         }
       }
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index d537c6b7a..cf72afcf6 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -518,7 +518,7 @@ class UsersController < ApplicationController
     user_fields = [:username, :upload_avatar_template, :uploaded_avatar_id]
     user_fields << :name if SiteSetting.enable_names?
 
-    to_render = { users: results.as_json(only: user_fields, methods: :avatar_template) }
+    to_render = { users: results.as_json(only: user_fields, methods: [:avatar_template, :letter_avatar_color]) }
 
     if params[:include_groups] == "true"
       to_render[:groups] = Group.search_group(term, current_user).map {|m| {:name=>m.name, :usernames=> m.usernames.split(",")} }
diff --git a/app/models/user.rb b/app/models/user.rb
index 2861fff88..aa46dd7c7 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -457,11 +457,11 @@ class User < ActiveRecord::Base
         avatar_template = split_avatars[hash.abs % split_avatars.size]
       end
     else
-      "#{Discourse.base_uri}/letter_avatar/#{username.downcase}/{size}/#{LetterAvatar.version}.png"
+      letter_avatar_template(username)
     end
   end
 
-  def self.avatar_template(username,uploaded_avatar_id)
+  def self.avatar_template(username, uploaded_avatar_id)
     return default_template(username) if !uploaded_avatar_id
     username ||= ""
     hostname = RailsMultisite::ConnectionManagement.current_hostname
@@ -469,11 +469,26 @@ class User < ActiveRecord::Base
   end
 
   def self.letter_avatar_template(username)
-    "#{Discourse.base_uri}/letter_avatar/#{username.downcase}/{size}/#{LetterAvatar.version}.png"
+    if SiteSetting.external_letter_avatars_enabled
+      color = letter_avatar_color(username)
+      "#{SiteSetting.external_letter_avatars_url}/letter/#{username[0]}?color=#{color}&size={size}"
+    else
+      "#{Discourse.base_uri}/letter_avatar/#{username.downcase}/{size}/#{LetterAvatar.version}.png"
+    end
+  end
+
+  def letter_avatar_color
+    self.class.letter_avatar_color(username)
+  end
+
+  def self.letter_avatar_color(username)
+    username = username || ""
+    color = LetterAvatar::COLORS[Digest::MD5.hexdigest(username)[0...15].to_i(16) % LetterAvatar::COLORS.length]
+    color.map { |c| c.to_s(16) }.join
   end
 
   def avatar_template
-    self.class.avatar_template(username,uploaded_avatar_id)
+    self.class.avatar_template(username, uploaded_avatar_id)
   end
 
   # The following count methods are somewhat slow - definitely don't use them in a loop.
diff --git a/app/serializers/basic_post_serializer.rb b/app/serializers/basic_post_serializer.rb
index 04b91ecad..4edb2b5cc 100644
--- a/app/serializers/basic_post_serializer.rb
+++ b/app/serializers/basic_post_serializer.rb
@@ -5,6 +5,7 @@ class BasicPostSerializer < ApplicationSerializer
              :username,
              :avatar_template,
              :uploaded_avatar_id,
+             :letter_avatar_color,
              :created_at,
              :cooked,
              :cooked_hidden
@@ -25,9 +26,14 @@ class BasicPostSerializer < ApplicationSerializer
     object.user.try(:uploaded_avatar_id)
   end
 
+  def letter_avatar_color
+    object.user.try(:letter_avatar_color)
+  end
+
   def cooked_hidden
     object.hidden && !scope.is_staff?
   end
+
   def include_cooked_hidden?
     cooked_hidden
   end
diff --git a/app/serializers/basic_user_serializer.rb b/app/serializers/basic_user_serializer.rb
index 8911291f3..12ed3f363 100644
--- a/app/serializers/basic_user_serializer.rb
+++ b/app/serializers/basic_user_serializer.rb
@@ -1,5 +1,5 @@
 class BasicUserSerializer < ApplicationSerializer
-  attributes :id, :username, :uploaded_avatar_id, :avatar_template
+  attributes :id, :username, :uploaded_avatar_id, :avatar_template, :letter_avatar_color
 
   def include_name?
     SiteSetting.enable_names?
@@ -17,4 +17,12 @@ class BasicUserSerializer < ApplicationSerializer
     object[:user] || object
   end
 
+  def letter_avatar_color
+    if Hash === object
+      User.letter_avatar_color(user[:username])
+    else
+      object.letter_avatar_color
+    end
+  end
+
 end
diff --git a/app/serializers/post_serializer.rb b/app/serializers/post_serializer.rb
index 5ba620ca2..9bc469f04 100644
--- a/app/serializers/post_serializer.rb
+++ b/app/serializers/post_serializer.rb
@@ -178,7 +178,8 @@ class PostSerializer < BasicPostSerializer
     {
       username: object.reply_to_user.username,
       avatar_template: object.reply_to_user.avatar_template,
-      uploaded_avatar_id: object.reply_to_user.uploaded_avatar_id
+      uploaded_avatar_id: object.reply_to_user.uploaded_avatar_id,
+      letter_avatar_color: object.reply_to_user.letter_avatar_color,
     }
   end
 
diff --git a/app/serializers/user_action_serializer.rb b/app/serializers/user_action_serializer.rb
index 8b3939963..4bf665004 100644
--- a/app/serializers/user_action_serializer.rb
+++ b/app/serializers/user_action_serializer.rb
@@ -27,9 +27,11 @@ class UserActionSerializer < ApplicationSerializer
              :edit_reason,
              :category_id,
              :uploaded_avatar_id,
+             :letter_avatar_color,
              :closed,
              :archived,
-             :acting_uploaded_avatar_id
+             :acting_uploaded_avatar_id,
+             :acting_letter_avatar_color
 
   def excerpt
     cooked = object.cooked || PrettyText.cook(object.raw)
@@ -84,4 +86,12 @@ class UserActionSerializer < ApplicationSerializer
     object.topic_archived
   end
 
+  def letter_avatar_color
+    User.letter_avatar_color(username)
+  end
+
+  def acting_letter_avatar_color
+    User.letter_avatar_color(acting_username)
+  end
+
 end
diff --git a/app/serializers/user_name_serializer.rb b/app/serializers/user_name_serializer.rb
index ac7beaa8d..3d7fc0d1f 100644
--- a/app/serializers/user_name_serializer.rb
+++ b/app/serializers/user_name_serializer.rb
@@ -1,20 +1,3 @@
-class UserNameSerializer < ApplicationSerializer
-  attributes :id, :username, :name, :title, :uploaded_avatar_id, :avatar_template
-
-  def include_name?
-    SiteSetting.enable_names?
-  end
-
-  def avatar_template
-    if Hash === object
-      User.avatar_template(user[:username], user[:uploaded_avatar_id])
-    else
-      object.avatar_template
-    end
-  end
-
-  def user
-    object[:user] || object
-  end
-
+class UserNameSerializer < BasicUserSerializer
+  attributes :name, :title
 end
diff --git a/app/serializers/user_serializer.rb b/app/serializers/user_serializer.rb
index 895453990..2d216a515 100644
--- a/app/serializers/user_serializer.rb
+++ b/app/serializers/user_serializer.rb
@@ -323,4 +323,5 @@ class UserSerializer < BasicUserSerializer
   def pending_count
     0
   end
+
 end
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index fcd190dc8..bfab232cf 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -979,6 +979,9 @@ en:
 
     avatar_sizes: "List of automatically generated avatar sizes."
 
+    external_letter_avatars_enabled: "Use external letter avatars service."
+    external_letter_avatars_url: "URL of the external letter avatars service."
+
     enable_flash_video_onebox: "Enable embedding of swf and flv (Adobe Flash) links in oneboxes. WARNING: may introduce security risks."
 
     default_invitee_trust_level: "Default trust level (0-4) for invited users."
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 754e067b8..add19d2db 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -572,6 +572,13 @@ files:
   avatar_sizes:
     default: '20|25|32|45|60|120'
     type: list
+  external_letter_avatars_enabled:
+    default: false
+    client: true
+  external_letter_avatars_url:
+    default: "https://avatars.discourse.org"
+    client: true
+    regex: '^https?:\/\/.+[^\/]$'
 
 trust:
   default_trust_level: