I know this is explicitly outside the stated scope of AMC, but note there is a lot of buzz currently about dark modes at the OS and browser levels.
Probably user demand for websites and apps to support these will soon increase dramatically.
The colour themes look great in the iOS app. I hope soon there will be two separate preferences, e.g. a user might want to read with Sepia at day and Black at night, with the OS changing from light to dark on a schedule or via ambient light sensor. Anyway, there seems to have been a lot of work done and solutions found for issues like branding and legibility.
Isarra and others have done some work on colour themes for various skins. I believe they use Extension:Theme? Is that extension ready for prime time on Wikimedia sites? And how hard would it be to make colour themes work with mobile/Minerva?
Im not expecting anybody to roll this into AMC, but is there high-level discussion happening somewhere about dark mode in general?