I believe the code currently uses about six colours. There's one for the list background, one for the border, two for list elements (red and blue) one for selected elements, and one for text. That's off the top of my head, so it may be a little off. I don't think there's much support for multiple highlight colours though, and I think it might take a bit of work to make them possible.
That said, it's a good idea. Definitely one to bear in mind.