There are humans who have four pigments in their color receptors but
they do not perceive a fourth primary color.

They just have increased distinction between the primary colors we
perceive. I take that to mean that they cannot point to anything in
nature as having a bright color that ordinary trichromats have never

Yeah I don't know the technical descriptions of what constitutes
primacy in hues, but it's not important to what I'm trying to get at.
The important thing is that the range and variety of colors we can see
or imagine is not explainable in purely quantitative or physical
terms, neither is it metaphysical, random, made up, or arbitrary. It
constitutes a visual semantic firmament, similar to the periodic
table. The differences between the color wheel and the periodic table
is that since experiences and feelings are phenomena that are
ontologically perpendicular to their external mechanics, they are not
strictly definable through literal observation and measurement, but
through first hand encounters which address the subject directly in a
more uncertain, figurative way. Colors look different depending on
what colors they are adjacent to, what mood we are in, our gender,
etc. unlike iron and magnesium which remain the same if placed next to
each other.

On Jul 11, 7:12 pm, meekerdb <> wrote:
> On 7/11/2011 3:29 PM, Craig Weinberg wrote:
> > I'm not talking about the idea of a primary color as linguistic
> > distinction, I'm talking about the inability of a color to be reduced
> > to combinations of other colors. Red, Green, and Blue are the primary
> > hues of projected light, Red, Yellow, and Blue are the primary hues of
> > reflected light.
> It's not the case that all colors can be reproduced by combinations of a
> fixed choice of red, green, and blue.  I refer you to pg 818 of Sears
> and Zemansky - my freshman physics text.  In any case, the fact that one
> can approximately match a color with an RGB mixture is a consequence of
> the human eye having three pigments in the color receptors.  If it had
> four, then you'd need another "primary" color.
> Brent

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