Re: Colors in Sherall

Sally Caves scripsit:

> Aha!  The additive (isn't it?) primary colors (that found in light):  red,
> green, and blue (white in the center), as opposed to the subtractive?
Subtractive, yes.

> primary colors (that found in paint): red, blue, and yellow (gray or black
> in the center)?   In the additive, red ovelapping green makes yellow; green
> overlapping blue makes... what?
Cyan, or aqua.

> and blue overlapping red makes...magenta?
Yes.

> In theory, a tetrachromat could tell the
> > difference between the yellow in a rainbow and any yellow (red/green
> > mixture) a monitor or TV could display.
>
> I don't get the difference.  I thought both were additive color.
The yellow in a rainbow is "real" yellow, in the sense that it reflects
a specific frequency of a light.  A false yellow such as you get from
a TV/monitor screen is a mixture of pure red and pure green with no
yellow light in it at all.  But the human eye can't tell the difference.
Similarly, the white light of the sun is an even mixture of all frequencies,
whereas the white light of "daylight fluorescent" is just a few specific
frequencies.  Again, the eye can't tell the difference.

> (In practice, due to the way
> > that tetrachromatism appears in humans, usually an extra copy of an
> > existing color gene, most human tetrachromats can only distinguish
> > between two close shades of green or red, and they're also usually
> > female.
>
> So they are color "blind"?
Not at all.  They can discriminate shades that you or I can't, but only
fairly subtle distinctions, not anywhere near as drastic as true vs.
false yellow.  Genetically, the red-sensitive and green-sensitive proteins
are closely related, and dichromatism (ordinary color blindness) is basically
having only one of the two, so red and green look the same.

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