Try a bunch of themes

gistfile1.js

let themes = [

'{"header":{"background":"#fff","text":"#000000"},"body":{"background":"#fff","text":"#4c4c4c","link":"#0079c1"},"button":{"background":"#0079c1","text":"#fff"},"logo":{"small":"https://arcgishub.maps.arcgis.com/sharing/rest/content/items/9d6a9bd32d0f480698f5cee208b27f90/data","link":"http://hub.arcgis.com"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#efefef","text":"#323232"}}',

'{"header":{"background":"#fff","text":"#000000"},"body":{"background":"#fff","text":"#4c4c4c","link":"#7245db"},"button":{"background":"#0079c1","text":"#fff"},"logo":{"small":"https://arcgishub.maps.arcgis.com/sharing/rest/content/items/9d6a9bd32d0f480698f5cee208b27f90/data","link":"http://hub.arcgis.com"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#efefef","text":"#000000"}}',

'{"header":{"background":"#e88140","text":"#ffffff"},"body":{"background":"#fef2ec","text":"#678096","link":"#000000"},"button":{"background":"#ffffff","text":"#ffffff"},"logo":{"small":"http://cggisw.coralgables.com/images/City Logo Horizontal White.png"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"flags":{"umbrella":false,"iframeheader":false,"customheader":true},"globalNav":{"background":"#e88140","text":"#ffffff"}}',

'{"button":{"background":"#0079c1","text":"#fff"},"fonts":{"heading":{"family":"Avenir Next","url":""},"base":{"family":"Avenir Next","url":""}},"flags":{"umbrella":false,"iframeheader":false,"customheader":false},"header":{"background":"#ffffff","text":"#000000"},"logo":{"small":"https://africageoportal.maps.arcgis.com/sharing/rest/content/items/1fc5b3d3b5a8420e81f163b6b5fdddce/data"},"body":{"background":"#ffffff","link":"#0079c1","text":"#4c4c4c"},"globalNav":{"background":"#ffffff","text":"#000000"}}',

'{"header":{"background":"#181818","text":"#ffffff"},"body":{"background":"#ffffff","text":"#4c4c4c","link":"#136fbf"},"button":{"background":"#136fbf","text":"#ffffff"},"logo":{"small":"https://maps1.brampton.ca/geohub/img/brampton-logo.png"},"flags":{"umbrella":false},"fonts":{"base":{"url":"https://fonts.googleapis.com/css?family=Quicksand","family":"Quicksand"},"heading":{"url":"https://fonts.googleapis.com/css?family=Quicksand","family":"Quicksand"}},"globalNav":{"background":"#181818","text":"#ffffff"}}',

'{"header":{"background":"#ffffff","text":"#0a1f33"},"body":{"background":"#ffffff","text":"#0a1f33","link":"#0a1f33"},"button":{"background":"#0a1f33","text":"#ffffff"},"logo":{"small":"https://gisonline.greenvillenc.gov/WebDocs/StoryMaps/G.png"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"flags":{"umbrella":false,"iframeheader":false,"customheader":true},"globalNav":{"background":"#ffffff","text":"#0a1f33"}}',

'{"header":{"background":"#ffffff","text":"#151515"},"body":{"background":"#ffffff","text":"#151515","link":"#ab060c"},"button":{"background":"#ab060c","text":"#ffffff"},"logo":{"small":"https://hub-coronavirus.s3.amazonaws.com/covid-19-gis-hub-social-share.jpg","link":"http://www.esri.com/services/disaster-response"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#007ac2","text":"#f8f8f8"}}',

'{"header":{"background":"#1c66a6","text":"#ffffff"},"body":{"background":"#f8f8f8","text":"#4c4c4c","link":"#136fbf"},"button":{"background":"#136fbf","text":"#ffffff"},"logo":{"small":"http://dashboards.syrgov.net/assets/Syracuse%20Logo%20with%20Fill%20white.png"},"flags":{"umbrella":false},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#1c66a6","text":"#ffffff"}}',

'{"header":{"background":"#002a53","text":"#ffffff"},"body":{"background":"#f8f8f8","text":"#4c4c4c","link":"#136fbf"},"button":{"background":"#136fbf","text":"#ffffff"},"logo":{"small":"https://s3.amazonaws.com/hifld-assets/images/hifld_logo_header_compressed.png"},"flags":{"umbrella":false,"iframeheader":false,"customheader":true},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#002a53","text":"#ffffff"}}',

'{"header":{"background":"#7f2629","text":"#ffffff"},"body":{"background":"#ffffff","text":"#4d4d4d","link":"#999999"},"button":{"background":"#719134","text":"#ffffff"},"logo":{"small":"https://iowadot.gov/gis/images/LOGO_WHITE.png"},"flags":{"umbrella":false},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#7f2629","text":"#ffffff"}}',

'{"header":{"background":"#e78e2e","text":"#505050"},"body":{"background":"#ffffff","text":"#505050","link":"#136fbf"},"button":{"background":"#1c66a6","text":"#fff"},"logo":{"small":"https://gis.johnscreekga.gov/images/datahub/logoSmall.png"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#fff","text":"#4c4c4c"}}',

'{"header":{"background":"#ffffff","text":"#272525"},"body":{"background":"#f8f8f2","text":"#272525","link":"#e80b0b"},"button":{"background":"#1c66a6","text":"#333"},"logo":{"small":""},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}}}',

'{"header":{"background":"#202883","text":"#ffffff"},"body":{"background":"#ffffff","text":"#202883","link":"#202883"},"button":{"background":"#202883","text":"#ffffff"},"logo":{"small":"http://mapleridge.ca/ImageRepository/Document?documentID=1613"},"flags":{"umbrella":false},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#202883","text":"#ffffff"}}',

'{"header":{"background":"#005E95","text":"#ffffff"},"body":{"background":"#ffffff","text":"#4c4c4c","link":"#0079c1"},"button":{"background":"#0079c1","text":"#fff"},"logo":{"small":""},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#005E95","text":"#ffffff"}}',

'{"button":{"background":"#136fbf","text":"#ffffff"},"fonts":{"heading":{"family":"Avenir Next","url":""},"base":{"family":"Avenir Next","url":""}},"flags":{"umbrella":false},"header":{"background":"#171717","text":"#000000"},"logo":{"small":"https://www.oakgov.com/it/gis/PublishingImages/Open%20Data%20Portal/Oakland%20County%20White.png"},"body":{"background":"#ffffff","link":"#136fbf","text":"#000000"},"globalNav":{"background":"#171717","text":"#000000"}}',

'{"header":{"background":"#ffffff","text":"#000000"},"body":{"background":"#ffffff","text":"#4c4c4c","link":"#0079c1"},"button":{"background":"#002663","text":"#ffffff"},"logo":{"small":"https://pbs.twimg.com/profile_images/134416207/flag_400x400.jpg"},"fonts":{"base":{"url":"https://cdn.esriuk.com/rnli/din/light.css?family=Din+Light","family":"Din Light"},"heading":{"url":"https://cdn.esriuk.com/rnli/din/light.css?family=Din+Light","family":"Din Light"}},"globalNav":{"background":"#ffffff","text":"#000000"}}',

'{"header":{"background":"#76afdf","text":"#000000"},"body":{"background":"#f8f8f8","text":"#4c4c4c","link":"#2a3b66"},"button":{"background":"#2a3b66","text":"#ffffff"},"logo":{"small":"http://www.cityofsacramento.org/-/media/Corporate/Images/Logos/SM_COStreatmentBLACK.png"},"flags":{"umbrella":false},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#76afdf","text":"#000000"}}',

'{"header":{"background":"#ffffff","text":"#000000"},"body":{"background":"#bdbdbd","text":"#4c4c4c","link":"#136fbf"},"button":{"background":"#176a8c","text":"#ffffff"},"logo":{"small":"http://i.imgur.com/FShPQeM.png"},"flags":{"umbrella":false},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#ffffff","text":"#000000"}}',

'{"header":{"background":"#141b4d","text":"#ffffff"},"body":{"background":"#f8f8f8","text":"#141b4d","link":"#c99700"},"button":{"background":"#c99700","text":"#000000"},"logo":{"small":"https://southbendin.gov/wp-content/uploads/2018/10/South-Bend-Seal-2016-RGB-e1540412252783.png"},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#141b4d","text":"#fff"}}',

'{"header":{"background":"#022a56","text":"#ffffff"},"body":{"background":"#f8f8f8","text":"#4c4c4c","link":"#136fbf"},"button":{"background":"#136fbf","text":"#ffffff"},"logo":{"small":"http://torontops.maps.arcgis.com/sharing/rest/content/items/b49d1583eb0e451b90380f8bfa6ae458/data"},"flags":{"umbrella":false,"iframeheader":false,"customheader":true},"fonts":{"base":{"url":"","family":"Avenir Next"},"heading":{"url":"","family":"Avenir Next"}},"globalNav":{"background":"#022a56","text":"#ffffff"}}',

'{"header":{"background":"#1c1c1c","text":"#ffffff"},"body":{"background":"#ffffff","text":"#000000","link":"#136fbf"},"button":{"background":"#136fbf","text":"#1c1c1c"},"logo":{"small":""},"flags":{"umbrella":false,"iframeheader":false,"customheader":true},"fonts":{"base":{"url":"https://fonts.googleapis.com/css?family=Lato","family":"Lato"},"heading":{"url":"https://fonts.googleapis.com/css?family=Lato","family":"Lato"}},"globalNav":{"background":"#1c1c1c","text":"#ffffff"}}'
].map(JSON.parse);

let themeIdx = 0;

let applyNextTheme = _ => {
  if (themeIdx >= themes.length) {
    alert('no more themes');
    return;
  }
  if (!$E.applyTheme) {
    alert('you must get a reference to the theme-generator service in $E using ember-inspector');
    return;
  }
  $E.applyTheme(themes[themeIdx]);
  themeIdx++;
};