Tetrachromats have colour vision based on four channels. Most humans have three channels (from the red, green and blue receptors in their eyes), while some colour-blind humans have only two channels. Some colour-weak humans with three channels with at least one of them shifted towards another.

To date, no scientifically verified tetrachromat has been identified.

The genetics for tetrachromacy and ColorBlindness are actually quite similar.  Red-green ColorBlindness and weakness is caused when a gene in the X-chromosome causes one's green receptors to be sensitive to the red part of the spectrum, or vice-versa.  This is why so few women are color-blind/weak; both X-chromosomes would require this gene.

Conversely, TetraChromat''''''s are ''exclusively'' female, since one requires both a color-weak and color-normal X-chromosome to be susceptible to tetrachromacy, and males usually have only one X-chromosome.  The condition relies on the errant color receptor to fall on the spectrum ''between'' red and green.

Imagine a version of ColorForth tailored for such people.

More details:

	* http://www.redherring.com/index.asp?layout=story&channel=70000007&doc_id=1910013991

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Tetrachromacy occurs when you have one female whose parents had two opposing variants of red-green colorweakness.

Red-green colorweakness occurs when green receptors are shifted in wavelength sensitivity towards red or vie versa, so while you can distinguish finer shades of yellow, tan and khaki you can't distinguish finer hue differences in the red-orange-yellow-green range, because there's nothing sensitive enough in that area of the spectrum. Likewise, there is blue-yellow colorweakness, where the perception of blue is shifted towards green.

Put one on one on your father's genes and the other on your mother's genes, and you get a tetrachromat.

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I must respectfully disagree.  I thought that red/green color blindness resulted from the lack of either the red or the green receptor?  The green receptor is a pretty good ways off in spectral sensitivity from the blue receptor.  Regards, Kenmce@spamcop.net

	* http://www.redherring.com/mag/issue86/mag-mutant-86.html


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As for me, I met this terminus first on the latest episode of "the three investigators" (German). I would like to contribute these three  links:

* http://ansuz.sooke.bc.ca/crossproduct/tetrachromat.html
* http://user.deluxnetwork.com/~zardoz/dna/col.html
* http://www.4colorvision.com/files/tetrachromat.htm

Additionally, I'll include the keyword: Tetrachromatism (German: Tetrachromatismus / Vierfarbensehen)

Cheers :)
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