I think Ellyn Eddy's "ABC - About Bunny Colors" is a fantastic resource for both beginners and those that have spent a lot of time working with rabbit coat color genetics. Last I checked you can get it on Amazon, rabbitsmarties.com or allthingsbunnies.com. It starts with basic Mendelian genetic inheritance and an intro to Punnet Square analysis, then covers the genetic codes for most rabbit coat colors. It doesn't get too much into trickier areas like effects of modifiers, but it really does a nice job of helping you figure out the basic functions and interactions of the most common color genes. It is a simple comb-bound booklet that has lots of color photos (though they're not the highest quality/resolution because of the printing), and leans more toward being a working rabbit breeder's guide than a theoretical one. But even if you want to learn more about genetics than just what applies to rabbit coat colors, Eddy's book gives you the basic principles and then uses coat color as a great example of how to apply those basic principles. I'd highly recommend it before trying Glenna Huffman's book, which I have but is definitely more theoretical and also directed squarely at rabbit coat colors (and which I use far less than "ABC" even though I've been working in genetics since, um, well let's say the last century, haha).
I agree with judymac that
Holland Lop Colors is a great site for info coat colors in normal fur.
Rabbit Genetics | The Nature Trail site offers a good basic intro but doesn't have many reference photos. Personally, I really like
Mini Rex Color Guide, which I probably use the most; it has both genetic codes and phenomenal color photos, especially useful in combination with GBFarm's page, since colors can look so different in normal vs rex coats. It's also a good resource in combination with "ABC" since the photos are better.