I was thinking camera when I wrote 'nice project idea' and that would be too much for me. But it is possible, someone at the Parallax forums built a Guitar Hero playing device. This thing is analyzing the video signal.
I didn't know that there are color sensors, that may be not too hard.
Edit:
Ooooh, a buddy of mine does IPhone apps for a living, I've posted him about it.I thought about writing a smart phone app that would take a picture of a resistor and tell you the value, but I just never did.