This is a book I had when I first started keeping rats as pets. Though not all inclusive, it does include some good varieties and genetic information. It is a good basis to start with. Keep in mind this book is using UK standards, so while the information is still good, the names of different colors may not be the same as those used here in the US.
http://www.amazon.com/The-Proper-Car...rats+nick+mays
I don’t know if there are any other good books out there, I would have to do some searching and then would have to read it myself before I'd feel comfortable recommending anything. AFRMA does have a genetics book that has pretty good information, but not all of it is completely accurate (such as their information about Burmese and BES varieties). That book can be purchased off their website, but may not be the best place to get started.
I personally like the information NFRS (UK based) provides. They do have publications, but I’m not sure where you might be able to find older issues. They have their standardized varieties posted on their website, including genotype (again some of the names will be different from what are used in the US). Once you get a basic understanding of the genes, you can look at their standards and figure out what gene combinations make what colors. Their standards are not inclusive of all possibilities, but do include a wide variety. Here is a link to their site with some information:
http://www.nfrs.org/sitemap.html
I think one of the best ways to learn is to just get in touch with experienced people and chat. You can see from this thread there are several individuals who have some great experience, and I’m sure some will let you pick their brains quite a bit. I would be happy to help out as well.