Dichromacy is color vision based on two functionally independent classes of photoreceptor input. Their different spectral sensitivities permit some optical spectra to be distinguished, but distinct spectra can still produce identical pairs of receptor responses and hence be metamers under the stated conditions.
A color matching experiment asks an observer to adjust primary lights to match a comparison field while controlling luminance cues. The available matches constrain the independent spectral information used by that observer. Two receptor classes do not mean that every appearance can be identified with one of only two named colors.
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Dichromacy is a type of color vision deficiency in which an individual is unable to perceive one of the three primary colors (red, green, or blue) due to the absence or dysfunction of one of the three types of cone photoreceptors in the retina. As a result, people with dichromacy are limited to seeing only two of the three primary colors, leading to a less varied color palette.