This sounds like it should be in Q&A. Maybe you're asking for a script to be written?
And the answer is that the colors are determined by the spot you enter the game. The first player is always red. Second is green and so on. There is no way to change that. And there is currently no script.
Chapcrap is right, it's not possible currently. I could write a script that does allow you to change colors for players (kinda hard though), but then again it would be confusing if someone else uses different colours and names the colours in chat.