I have taken color classes and own several books, but I agree with Ninnie - it's really all about contrast.
With colors, I do tend to separate "white" colors from "beige" colors when I make a quilt, except in really scrappy quilts, but otherwise I just play around.
Oh, and I found that making miniature and other small projects was a good wasy to experiment with different fabric combinations, because they didn't require a large investment in time or money.