Also, within that link from equadorian there is another moethod described for doing this. It is VERY useful, especially if you want more than 2 colors, or don't want hundreds of materials added to your material browser. The specific post is here:
http://www.sketchucation.com/forums/scf/viewtopic.php?f=180&t=16660&st=0&sk=t&sd=a&start=15#p131738
Chris