I'm not sure how much comparison there is between hair color in humans and fur color in dogs, but here goes. I saw a program on dog evolution some months back: http://www.pbs.org/wgbh/nova/dogs/about.html

It reported on an interesting experiment on foxes that occurred in Russia. They were attempting to produce less ferocious foxes they could release in the wild, but surprisingly they produced foxes with many colors and different sizes, as well. (That was a very small part of the entire program.)