This image illustrates the three "Base" colours that all other colours act upon. Yes, I am aware that Bay is not a true base, but when considering the dilutions, it makes sense to call it a base. So I am.
Part Two: The Cream Gene [link]
Part Three: The Champagne Gene [link]
Part Four: The Dun Gene [link]
Part Five: The Silver Gene [link]
Part Six: White Patterns [link]