AS is already mentioned before,
it is probably because of 2 reasons (whatever you please):
- in some of those old asian movies (mostly with english subs) the subtitles are in different colours. It could to contrast with a certain background. but…
- another reason is to indicate who is speaking. someone stated that we arent’ and I quote “Whoever can’t figure out who’s talking without colorizing the text should jump off a mountain. Seriously, it’s like “Do you wish to penetrate me?” HMMM I WONDER WHO’S TALKING, FUCKING MORONS” well mr., they actually really do use different subs do indicate who is speaking. it could be because they think we can’t connect the voice to the face, or if 2 people are onscreen and they speak through each other or simultanuously, different colours are used to indicate this.
these are pretty much the reasons why have different colours officialy, now it could be that Kill Bill does it for the same reason, but I think a more obvious reason is to mimick to old movies with the coloured subs.