Tetrachromacy

Color vision defined in 4 dimensions (generally, have 4 different types of Cones). There are two types of Tetrachromats:

• Weak – the individual has 4 cones, but they do not have 4 dimensional color vision and their Gamut can be fully covered using 3 Primary Colors. In Humans, Carriers of Protanomaly and Deuteranomaly have 4 Opsins expressed in their Retina, but the the L*/M* Opsin generally maps to the same channel as the L/M Opsin, so they are still functionally Trichromatic.
• Strong – the individual has at least 4 cones and they need four Primary Colors to generate their entire Gamut. Many animals are Strong Tetrachromats (e.g. birds and insects). No humans have been convincingly shown to be.

The Chromaticity Diagram of a Tetrachromat is 3-Dimensional, compared to the 2-Dimensional Standard Observer Chromaticity Diagram.

See also Pentachromacy.