diff --git a/src/components/structures/MatrixChat.js b/src/components/structures/MatrixChat.js
index a185664038..9392a14ad4 100644
--- a/src/components/structures/MatrixChat.js
+++ b/src/components/structures/MatrixChat.js
@@ -56,6 +56,7 @@ import { ValidatedServerConfig } from "../../utils/AutoDiscoveryUtils";
 import AutoDiscoveryUtils from "../../utils/AutoDiscoveryUtils";
 import DMRoomMap from '../../utils/DMRoomMap';
 import { countRoomsWithNotif } from '../../RoomNotifs';
+import { setTheme } from "../../theme";
 
 // Disable warnings for now: we use deprecated bluebird functions
 // and need to migrate, but they spam the console with warnings.
@@ -658,7 +659,7 @@ export default createReactClass({
                 break;
             }
             case 'set_theme':
-                this._onSetTheme(payload.value);
+                setTheme(payload.value);
                 break;
             case 'on_logging_in':
                 // We are now logging in, so set the state to reflect that
@@ -1102,82 +1103,6 @@ export default createReactClass({
         });
     },
 
-    /**
-     * Called whenever someone changes the theme
-     *
-     * @param {string} theme new theme
-     */
-    _onSetTheme: function(theme) {
-        if (!theme) {
-            theme = SettingsStore.getValue("theme");
-        }
-
-        // look for the stylesheet elements.
-        // styleElements is a map from style name to HTMLLinkElement.
-        const styleElements = Object.create(null);
-        let a;
-        for (let i = 0; (a = document.getElementsByTagName("link")[i]); i++) {
-            const href = a.getAttribute("href");
-            // shouldn't we be using the 'title' tag rather than the href?
-            const match = href.match(/^bundles\/.*\/theme-(.*)\.css$/);
-            if (match) {
-                styleElements[match[1]] = a;
-            }
-        }
-
-        if (!(theme in styleElements)) {
-            throw new Error("Unknown theme " + theme);
-        }
-
-        // disable all of them first, then enable the one we want. Chrome only
-        // bothers to do an update on a true->false transition, so this ensures
-        // that we get exactly one update, at the right time.
-        //
-        // ^ This comment was true when we used to use alternative stylesheets
-        // for the CSS.  Nowadays we just set them all as disabled in index.html
-        // and enable them as needed.  It might be cleaner to disable them all
-        // at the same time to prevent loading two themes simultaneously and
-        // having them interact badly... but this causes a flash of unstyled app
-        // which is even uglier.  So we don't.
-
-        styleElements[theme].disabled = false;
-
-        const switchTheme = function() {
-            // we re-enable our theme here just in case we raced with another
-            // theme set request as per https://github.com/vector-im/riot-web/issues/5601.
-            // We could alternatively lock or similar to stop the race, but
-            // this is probably good enough for now.
-            styleElements[theme].disabled = false;
-            Object.values(styleElements).forEach((a) => {
-                if (a == styleElements[theme]) return;
-                a.disabled = true;
-            });
-            Tinter.setTheme(theme);
-        };
-
-        // turns out that Firefox preloads the CSS for link elements with
-        // the disabled attribute, but Chrome doesn't.
-
-        let cssLoaded = false;
-
-        styleElements[theme].onload = () => {
-            switchTheme();
-        };
-
-        for (let i = 0; i < document.styleSheets.length; i++) {
-            const ss = document.styleSheets[i];
-            if (ss && ss.href === styleElements[theme].href) {
-                cssLoaded = true;
-                break;
-            }
-        }
-
-        if (cssLoaded) {
-            styleElements[theme].onload = undefined;
-            switchTheme();
-        }
-    },
-
     /**
      * Starts a chat with the welcome user, if the user doesn't already have one
      * @returns {string} The room ID of the new room, or null if no room was created
diff --git a/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js b/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
index b9c566b22a..64aafe6046 100644
--- a/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
+++ b/src/components/views/settings/tabs/user/GeneralUserSettingsTab.js
@@ -27,7 +27,7 @@ import LanguageDropdown from "../../../elements/LanguageDropdown";
 import AccessibleButton from "../../../elements/AccessibleButton";
 import DeactivateAccountDialog from "../../../dialogs/DeactivateAccountDialog";
 import PropTypes from "prop-types";
-import {THEMES} from "../../../../../themes";
+import {enumerateThemes} from "../../../../../theme";
 import PlatformPeg from "../../../../../PlatformPeg";
 import MatrixClientPeg from "../../../../../MatrixClientPeg";
 import sdk from "../../../../..";
@@ -275,8 +275,8 @@ export default class GeneralUserSettingsTab extends React.Component {
                 <span className="mx_SettingsTab_subheading">{_t("Theme")}</span>
                 <Field id="theme" label={_t("Theme")} element="select"
                        value={this.state.theme} onChange={this._onThemeChange}>
-                    {Object.entries(THEMES).map(([theme, text]) => {
-                        return <option key={theme} value={theme}>{_t(text)}</option>;
+                    {Object.entries(enumerateThemes()).map(([theme, text]) => {
+                        return <option key={theme} value={theme}>{text}</option>;
                     })}
                 </Field>
                 <SettingsFlag name="useCompactLayout" level={SettingLevel.ACCOUNT} />
diff --git a/src/settings/Settings.js b/src/settings/Settings.js
index e0ff16c538..c82b7a0c71 100644
--- a/src/settings/Settings.js
+++ b/src/settings/Settings.js
@@ -245,6 +245,10 @@ export const SETTINGS = {
         default: "light",
         controller: new ThemeController(),
     },
+    "custom_themes": {
+        supportedLevels: LEVELS_ACCOUNT_SETTINGS,
+        default: [],
+    },
     "webRtcAllowPeerToPeer": {
         supportedLevels: LEVELS_DEVICE_ONLY_SETTINGS_WITH_CONFIG,
         displayName: _td('Allow Peer-to-Peer for 1:1 calls'),
diff --git a/src/settings/controllers/ThemeController.js b/src/settings/controllers/ThemeController.js
index da20521873..a15b4e78cd 100644
--- a/src/settings/controllers/ThemeController.js
+++ b/src/settings/controllers/ThemeController.js
@@ -16,12 +16,13 @@ limitations under the License.
 */
 
 import SettingController from "./SettingController";
-import {DEFAULT_THEME, THEMES} from "../../themes";
+import {DEFAULT_THEME, enumerateThemes} from "../../theme";
 
 export default class ThemeController extends SettingController {
     getValueOverride(level, roomId, calculatedValue, calculatedAtLevel) {
+        const themes = enumerateThemes();
         // Override in case some no longer supported theme is stored here
-        if (!THEMES[calculatedValue]) {
+        if (!themes[calculatedValue]) {
             return DEFAULT_THEME;
         }
 
diff --git a/src/theme.js b/src/theme.js
new file mode 100644
index 0000000000..c2baca67da
--- /dev/null
+++ b/src/theme.js
@@ -0,0 +1,139 @@
+/*
+Copyright 2019 Michael Telatynski <7t3chguy@gmail.com>
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {_t} from "./languageHandler";
+
+export const DEFAULT_THEME = "light";
+import Tinter from "./Tinter";
+import SettingsStore from "./settings/SettingsStore";
+
+export function enumerateThemes() {
+    const BUILTIN_THEMES = {
+        "light": _t("Light theme"),
+        "dark": _t("Dark theme"),
+    };
+    const customThemes = SettingsStore.getValue("custom_themes");
+    const customThemeNames = {};
+    for (const {name} of customThemes) {
+        customThemeNames[`custom-${name}`] = name;
+    }
+    console.log("customThemeNames", customThemeNames);
+    return Object.assign({}, customThemeNames, BUILTIN_THEMES);
+}
+
+function setCustomThemeVars(themeName) {
+    // set css variables
+    const customThemes = SettingsStore.getValue("custom_themes");
+    if (!customThemes) {
+        throw new Error(`No custom themes set, can't set custom theme "${themeName}"`);
+    }
+    const customTheme = customThemes.find(t => t.name === themeName);
+    if (!customTheme) {
+        const knownNames = customThemes.map(t => t.name).join(", ");
+        throw new Error(`Can't find custom theme "${themeName}", only know ${knownNames}`);
+    }
+    const {style} = document.body;
+    if (customTheme.colors) {
+        for (const [name, hexColor] of Object.entries(customTheme.colors)) {
+            style.setProperty(`--${name}`, hexColor);
+            // uses #rrggbbaa to define the color with alpha values at 0% and 50%
+            style.setProperty(`--${name}-0pct`, hexColor + "00");
+            style.setProperty(`--${name}-50pct`, hexColor + "7F");
+        }
+    }
+}
+
+/**
+ * Called whenever someone changes the theme
+ *
+ * @param {string} theme new theme
+ */
+export function setTheme(theme) {
+    if (!theme) {
+        theme = SettingsStore.getValue("theme");
+    }
+    let stylesheetName = theme;
+    if (theme.startsWith("custom-")) {
+        stylesheetName = "light-custom";
+        const themeName = theme.substr(7);
+        setCustomThemeVars(themeName);
+    }
+
+    // look for the stylesheet elements.
+    // styleElements is a map from style name to HTMLLinkElement.
+    const styleElements = Object.create(null);
+    let a;
+    for (let i = 0; (a = document.getElementsByTagName("link")[i]); i++) {
+        const href = a.getAttribute("href");
+        // shouldn't we be using the 'title' tag rather than the href?
+        const match = href.match(/^bundles\/.*\/theme-(.*)\.css$/);
+        if (match) {
+            styleElements[match[1]] = a;
+        }
+    }
+
+    if (!(stylesheetName in styleElements)) {
+        throw new Error("Unknown theme " + stylesheetName);
+    }
+
+    // disable all of them first, then enable the one we want. Chrome only
+    // bothers to do an update on a true->false transition, so this ensures
+    // that we get exactly one update, at the right time.
+    //
+    // ^ This comment was true when we used to use alternative stylesheets
+    // for the CSS.  Nowadays we just set them all as disabled in index.html
+    // and enable them as needed.  It might be cleaner to disable them all
+    // at the same time to prevent loading two themes simultaneously and
+    // having them interact badly... but this causes a flash of unstyled app
+    // which is even uglier.  So we don't.
+
+    styleElements[stylesheetName].disabled = false;
+
+    const switchTheme = function() {
+        // we re-enable our theme here just in case we raced with another
+        // theme set request as per https://github.com/vector-im/riot-web/issues/5601.
+        // We could alternatively lock or similar to stop the race, but
+        // this is probably good enough for now.
+        styleElements[stylesheetName].disabled = false;
+        Object.values(styleElements).forEach((a) => {
+            if (a == styleElements[stylesheetName]) return;
+            a.disabled = true;
+        });
+        Tinter.setTheme(theme);
+    };
+
+    // turns out that Firefox preloads the CSS for link elements with
+    // the disabled attribute, but Chrome doesn't.
+
+    let cssLoaded = false;
+
+    styleElements[stylesheetName].onload = () => {
+        switchTheme();
+    };
+
+    for (let i = 0; i < document.styleSheets.length; i++) {
+        const ss = document.styleSheets[i];
+        if (ss && ss.href === styleElements[stylesheetName].href) {
+            cssLoaded = true;
+            break;
+        }
+    }
+
+    if (cssLoaded) {
+        styleElements[stylesheetName].onload = undefined;
+        switchTheme();
+    }
+}
diff --git a/src/themes.js b/src/themes.js
deleted file mode 100644
index 2529a04d89..0000000000
--- a/src/themes.js
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
-Copyright 2019 Michael Telatynski <7t3chguy@gmail.com>
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-import {_td} from "./languageHandler";
-
-export const DEFAULT_THEME = "light";
-
-export const THEMES = {
-    "light": _td("Light theme"),
-    "dark": _td("Dark theme"),
-    "light-custom": _td("Custom theme (light)"),
-};