Color contrast

Color contrast is the perceived difference between colors viewed side by side or in comparison. It depends on properties such as hue, lightness, and saturation, as well as viewing conditions.

Simultaneous contrast: A perceptual effect in which a color’s appearance shifts according to the color surrounding it. It is the clearest case of adjacent colors changing one another’s perceived appearance.
Hue: The attribute of color associated with categories such as red, green, or blue. Adjacent hues can contrast even when their lightness and saturation are similar.
Web Content Accessibility Guidelines: International guidelines for making web content more accessible to people with disabilities. Their contrast criteria address whether text remains distinguishable from its background.
Color harmony: Aesthetic judgments about how colors combine within a composition. Harmony concerns the quality of a color combination, while contrast describes perceived difference.
Successive contrast: A perceptual effect in which viewing one color alters the appearance of a color seen afterward. It shows that contrast can persist across time rather than require adjacent patches.
Lightness: The perceived degree to which a color appears light or dark. Lightness differences often determine whether colors remain distinct at small sizes.
Contrast ratio: A numerical comparison of the luminance of two colors, commonly used to assess text legibility. It provides a practical luminance-based test for foreground and background separation.
Color balance: The adjustment or arrangement of colors to achieve a desired overall appearance. Balance concerns the composition as a whole rather than the difference between particular colors.
Color constancy: The visual system’s tendency to perceive object colors as stable despite changes in illumination. Constancy and contrast both depend on interpreting colors relative to illumination and surroundings.
Saturation: The perceived intensity or purity of a color relative to a neutral gray. Saturation differences create contrast that can remain subtle when lightness is equal.

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