Trichromacy or trichromaticism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats.
According to the trichromatic theory of color vision, also known as the Young-Helmholtz theory of color vision, there are three receptors in the retina that are responsible for the perception of color. One receptor is sensitive to the color green, another to the color blue and a third to the color red.
Most people are trichromats, possessing three types of cone cells to see color with. A woman in northern England has four types of working cone cells, which means she has the ability to see far more colors than most of us can.
Article at https://futurism.com/uk-woman-extra-cone-cell-her-eyes-can-see-more-colors/