Complementary colors are sometimes used together to create maximum attention but are inclined to clash, in particular green and red. When one complementary color is used for text against the other's background it is difficult to read the type.
Complementary colors are opposite each other on the color wheel.
Complementary pairs contrast because they do not share any common colors. Complementary colors are inclined to vibrate when placed next to each other.
Mixing one complementary color with a portion of the other desaturates the color with the larger portion.