a deficiency of color vision in which the person can match any given hue by mixing only two other wavelengths of light (as opposed to the three wavelengths needed by people with normal color vision)

Condition of possessing two independent channels for conveying color information. Color matching for dichromats requires only two primaries. Most "color blind" humans are dichromats and have lost the function of one of the cone types and consequently one of the opponent processes. Dichromats are not strictly color blind in the sense that their vision is sensitive to a single chromatic dimension as well as to brightness.

Dichromacy in humans is a moderately severe color vision defect in which one of the three basic color mechanisms is absent or not functioning. It is hereditary and sex-linked, affecting predominantly males.Cassin, B. and Solomon, S. Dictionary of Eye Terminology.