For anyone browsing Links Beat, here is a clear starting point on the subject.
A colour wheel arranges colours in a circle so their relationships are easy to see, and it takes much of the guesswork out of decorating. Neighbouring colours, such as blue and green, create a calm, harmonious room. Colours opposite each other, such as blue and orange, create contrast and energy, and work best when one dominates and the other appears in small accents.