dichromatic

Dichromatic is an adjective used across science and art to describe something that involves two colors or two color components. The term derives from Greek roots meaning “two colors.”

In optics, dichromatic light refers to light composed of two distinct wavelengths. Dichroic filters and materials can transmit, reflect, or absorb two spectral regions in different ways, producing effects such as color separation or two-tone appearances. In color theory and design, a dichromatic palette uses two colors, often chosen for contrast or harmony in an artwork or composition. In printing and imaging, dichromatic processes may reproduce images with two inks or tones, creating duotone or limited-color effects.

In vision and biology, dichromatic color vision means the presence of only two functional cone photopigments in the eye, rather than the three found in typical human trichromacy. This condition, known as dichromacy, yields a two-dimensional color perception and can reduce the ability to distinguish certain hues. In humans, the most common form is red-green dichromacy, resulting from the absence or nonfunction of either the long-wavelength (L) or middle-wavelength (M) cone pigment. A rarer form is blue-yellow dichromacy (tritanopia), caused by lack of short-wavelength (S) cones. Many non-primate mammals are naturally dichromats, while birds and some other animals may be tetrachromats or more.

Dichromatic concepts thus span practical uses in lighting and printing, perceptual differences in vision, and artistic applications, reflecting the common theme of two-color interplay.