The colors were introduced for distinction, to speed up hopping from bug to bug of a certain type. I decided against coloring the legend because it(probably, didn't try) looks ugly and because in my view it was not important which color ITP is. But that's just my view. I plan to open up the source soon so you will be able to play with that :-)
A minor niggle, but the colours you have chosen are not good for the 5% of your male viewers who have deuteranopia or protanopia, the two most common forms of colour-blindness. I don't have either condition myself, but I've been bitten by this before in web pages I've created... in particular the green and yellow shades are almost identical for people with either condition.
Tim --The Wellcome Trust Sanger Institute is operated by Genome Research Limited, a charity registered in England with number 1021457 and a company registered in England with number 2742969, whose registered office is 215 Euston Road, London, NW1 2BE.