Tetrachromia (of tetra - "four" - and chroma - "color" -) is a visual characteristic: tetrachromats see more colors than usual because they have four types of color receptors, when it is usual to have three.
Tetrachromia occurs only in women, with a prevalence of around 18% of the female population.
Although it is common to use the term indistinctly with "four-color", it should not be confused with this, which is a procedure used in graphic arts, especially in photogravure, to obtain all colors from four fundamental colors. It is made from the trichrome by increasing a fourth clisé to obtain black (a "non-color", but gives intensity and allows a more faithful reproduction of the original). Notes
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