Hehe. Sorry last time i looked RAT just had the color blend setting where the intermediate colors where generated automagicaly (i assume). Even now though users could just know that they need to supply a a. and a td. class for each color they wanted to set. I think that then CSS could even be used to insert the char into the table cell (i'm thinking the way some of use insert symbols in front of other users names in the CB).
I don't see any need to parse users input at all, if they are over ridding the actual CSS then they need to get all the tags, and if they are using the color blend then the site generates the needed CSS. Am I missing something painfully obvious? ;)