Physics: Problems and Solutions
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yellow yellow-
green
green cyan blue violet purple magenta red red-orange orange orange-
yellow
                       
FF0 8F0 0F0 0FF 00F 80F F0F F08 F00 F40 F80 FC0
000F 0F00 0FF0 00F0 F000
FF0 0F0 00F F00
0F00 000F 00FF 00F0 F000
0F0 000 00F F00


The primary colors that the brain (not the retina) perceives are

yellow
red
blue

combining these gives the secondary colors

orange
purple
green

One can see that these colors are intermediate between the primary colors

One would assume then that combining a primary color and a secondary color would result in a color intermediate between the primary and the secondary. And indeed most do. Except for cyan.

Cyan is not intermediate between blue and green. It is clearly a combination of blue and something. But what that something is is not clear.

I suggest that there were originally four primary colors. Cyan is between blue and the fourth primary color which no longer exists.

Retina

The original four color receptors were

yellow
green
red
blue

Except we didnt perceive the green receptor as green. We perceived it as a fourth primary color that no longer exists

Eventually we started perceiving the output of the green receptor as between yellow and blue. So we no longer needed four light receptors in the retina. So we dropped one. But instead of dropping the green receptor we dropped the yellow receptor.

Origin of the colors

Yellow, red, and blue are colorized, beautified versions of white, grey, and black. It isnt clear what the fourth primary color corresponded to.

white yellow
grey red
black blue
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