Deb Menz's Color in Spinning is a practical book for all of the color cowards, like me, out there. You can buy it directly from her through that link above, by the way.
Chapter One is a great overview of general color theory, including the color principles that are most useful to spinners.
In fact, for anyone who doesn't have a firm grasp of clor theory (that's me, again), the color wheels, alone, are worth the price of admission for this book.
Deb also helps me overcome my reluctance to just try something already by offering self-study exercises in color. They can be executed with paint, paper, dye, or fibers. The first set has 20 different variations to try.
Even if you don't want to dye your own fiber or blend colors with cards or combs (and if you do, this is really a must-own book), the last chapter offers a chance to explore color changes in plying, by mixing and matching either six or eight different singles.
The last chapter is a gallery of finished objects that ranges from sweaters to a parrot sculpture. Even if the sweaters aren't your style and you don't have a use for a non-talking painted silk parrot, it is really interesting to see the different color combinations.
Color in Spinning is a large, coffee-table style of book, but it is also an articulate and practical guide to the world of color in fiber.