Is it possible to implement the support of coloured subtitles? What it mean is not to change to a static colour but to display subs that have multiple colours for the various speech on screen. I know plex/emby supports this but can not see any options in infuse, maybe a default options for colour?
Yes, if you are using SSA/ASS subtitles which can include advanced subtitle formatting Infuse will be able to recognize these stylings and colors.
For regular text-based subtitles (like SRT) which typically don’t have color information you would be able choose from a list of available colors which would apply to all subtitles.