"fine, all colors are specified in RGB, CMYK, HSV, HSL, YCbCr or XYZ" -- YIQ, YUV, composite

"all subtitle files are UTF-8 encoded" -- EIA-608, EIA-708, graphics only (DVD subtitles)

"all subtitles are stored/rendered as RGB" -- DVD subtitles use indexed colours with a specified palette which isn't RGB, I think.