Thanks for the great explanation of the OpenType color tables!
Just a quick note: COLR/CPAL also works in Firefox on all systems. And Microsoft will soon support all formats in Windows 10, so that’s great news! You can check support for your browser/OS in a little test I made: https://pixelambacht.nl/chromacheck/ (the code is on Github too).
As pointed out the me recently, now the proposals have become a standard, they’re not really anyone’s “property” anymore. They’re now OpenType CBDT/CBLC, COLR, CPAL and SVG. Sbix is is the only non-standard format left, because currently it proprietary Apple. I still need to change that in ChromaCheck :)