Complementary pairs contrast because they share no common colors.
For example, red and green are complements, because green is made of blue and yellow. Complementary colors can appear very exciting and seem to vibrate when placed side by side. By placing brilliant orange flowers against a bright blue background, Vincent van Gogh's painting buzzes with visual energy. Because van Gogh did not smooth his brush strokes, it's easy to see how he used complementary pairs. The red of the flowers contrasts with the green of the leaves.