An optical effect caused by the tendency of contrasting forms and colors to emphasize their difference when they are placed together.
An idea that our perception of a color or apparent value is influenced by the background against which the color or value is seen. e.g. a gray glove placed on a black ground looks bright, but the same glove placed on white, snowy ground appears much darker.
When two different color tones come into direct contact, the contrast intensifies the difference between them.