Complementary colours exhibit the highest possible contrast with each other.
In practice, complementary colours are those that exhibit the highest level of contrast with each other. For painters, the fundamental complementary pairs are red/green, yellow/violet, and blue/orange, while each intermediate colour also possesses its unique complement. The colour wheel organises all visible spectrum colours in such a way that complementary pairs are directly opposite each other.
In painting, artists leverage complementary colours for their striking contrasts and the way they mutually enhance each other when placed side by side. This is employed for creating vibrant draperies or for adding a hint of the complementary colour to shadows adjacent to highlights. This technique mimics the way the human eye responds to colour and was frequently used by Impressionist and Post-Impressionist artists.