The colour wheel illustrates important relationships between colours. It shows how colours harmonize when they are close in hue, saturation and lightness. Closeness in any one of these three characteristics contributes to harmony. Adjacent hues on the colour wheel therefore harmonize successfully, as may the lighter tints of different hues.
Hues on opposite sides of the colour wheel are complementary - in theory, if they are added together they produce white. In practice, they are pairs of colours with maximum contrast. These, and others hues that are widely separated on the colour wheel, provide effective colour contrast. If used together in a photograph they may clash in an unacceptable manner, but when used wisely they may produce striking contrasts and vibrant images.