Here's two breeder's sites I've found useful for understanding Campbell's genetics.
Odds and Endlers - a Florida hamster breeder, easy to understand pages on Campbell's genetics
http://www.geocities.com/florida_hamster/
Linda Price's AAA hamstery - very comprehensive, picture galleries of all the colours and genetics, plus pages about new genes that she is working with. Lots of information on the other hamster species too.
http://www.geocities.com/aaahamsters/