This is in many ways a more simplified version of Itten’s exhaustive The Art of Color. If you plan to work with color at all, you owe it to yourself to know some decent color principles like why certain color combinations work better than others, theories on color contrasts and processes to obtain color combinations that evoke particular moods. Also check out: Color Index by Jim Krause, and Leslie Cabarga’s The Designer’s Guide to Color Combinations and The Designer’s Guide to Global Color Combinations. While these are useful, they can also become crutches. Use them as starting points to color ideas or as reference.