I just found this webinar about how colors work together for quilts. It's really full of information and helps you understand how to pick colors to get the effect you want, and why some things work and some don't. I learned a lot. It's about 2 hours long, so watch it when you have the time, it's only going to be available for a few days, so if you are interested, it's well worth the time.
http://www.thequiltingcoach.com/public/918.cfm?sd=64