Look Inside the Eye
Color vision can be defined by what kind of color-detecting equipment exists inside the eye of a human or non-human animal. Some species see no colors, some see a few colors, some see all colors, and some see colors that are not visible to the typical human eye.
The color-detecting equipment inside an eye is called a "cone."
(The rods are for night vision.)
The number of visible colors is defined by the kinds of cones in the eye.
|Humans have three kinds of color receptor cells - or “cones” - in their eyes. Each type of cone contains a different visual pigment. These three cone types are called "red", "green" and "blue." Therefore we are “trichromats” (tri = 3, chroma = color).|
All hues can be produced by mixing red, green and blue light. This is how a color television set works; a mixture of these three wavelengths of color produces several million visible colors.)
(with a special sensitivity to ultraviolet)
|Some animals - for example bees - have three types of cones. Two of the cones are sensitive to "human visible" wavelengths. The third cone is sensitive to colors in the ultraviolet range of the spectrum.|
This cone enables them to see colors that humans can’t see.
They also perceive human-visible spectra in different hues than those that humans experience. Source
|Most bird species (that have been studied) have at least four types of cones. They are "tetrachromats." Recent studies have confirmed tetrachromacy in some fish and turtles.|
Perhaps it is mammals, including humans, that have poor color vision! Source
|It has been suggested that some women are also tetrachromats One study suggested that 2-3% of the world's women may have the kind of fourth cone that gives a significant increase in color differentiation. Source|
Another thing to considered: Some data suggests that the architecture of the human visual system (as well as that of many animals) is really tetrachromatic - but that this capacity is blocked. Source
|Many animals have only two kinds of cones in their eyes. They are known as “dichromats.” It’s worth noting that the color-sensing pigment in these cones may be weak. Therefore, an animal - for example a dog - probably sees very weak colors.|
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Neuroscience for Kids - Color Vision
Purple is the hardest color for the eye to discriminate. Some say it's a supernatural color. Others say it's really just a happy color. Find out more at Color Matters: Purple