Dichromacy (
di meaning "two" and
chroma meaning "color") is the state of having two types of functioning
color receptors, called
cone cells, in the
eyes. Organisms with dichromacy are called dichromats. Dichromats can match any color they see with a mixture of no more than two pure
spectral lights. By comparison,
trichromats require three pure spectral lights to match all colors that they can perceive, and
tetrachromats require four.