Stylized captions are now broken

[EmmettLuis]

YouTube had been using SRV3, its own proprietary caption system for the last few years, and it was really powerful since it effectively combined the ideas and results of various other subtitle languages. This included positions, styles (bold, italic, etc.), and colors.
As of the last 2 hours, on browsers, YouTube has rolled out a JSON-based caption processor instead of its original XML-based. In the process... quoting a fellow subtitler now:

this format only allows a very limited set of colors (RGB CMY WB). If you use a color that's not allowed, it uses white instead - so white text on a pink background becomes white text on a white background (because pink is not allowed)
So if they send the original XML format to your browser, all colors work, but if they send you the new JSON format, most colors don't work