If a new template requires a fourth color, a lot of logic needs to be repeated to allow it.
Each template should specify an array of colors and the app should just show color pickers for those colors.
We're missing a service worker with a fetch event handler to meet the PWA criteria.
If you go to Dev Tools > Application > Add to homescreen you'll currently get Site cannot be installed: no matching service worker detected. You may need to reload the page, or check that the service worker for the current page also controls the start URL from the manifest