KeithK wrote:

In article ,
(Kevin Brooks) wrote:



I believe what he was referring to is the fact that red, green, and
blue are *the* primary colors.

Er, isn't that red, green, and yellow?

There is no such thing as "the primary" colours.


Colour is a very subjective thing.

If you're dealing with paint it would be red, blue and yellow (or Cyan,
Magenta and Yellow)
If dealing with light the most commonly used one would be red, blue and
green (RGB)

The human eye contains two different types of light receptive cells:
so-called cones and rods. Cones are used in light with relatively high
intensities and are responsible for colour vision. Visible light is only
a very small part of the electromagnetic spectrum, between 380 and 700
nm. Light of a certain spectral wavelength appears to us as a colour,
but light from a single wavelength is not the only way to create the
sensation of that particular colour. Different spectral distributions
can produce an indistinguishable colour sensation. The commonly accepted
theory for how colour vision works is that the cones in the human eye
contain three different pigments, with three different absorption
spectra: a pigment most sensitive to light around 450 nm (blue), one
most sensitive to light with a wavelength of 550 nm (green/yellow) and
one most sensitive near 570 nm (yellow/orange). That is why combinations
of three primaries, for instance red, green and blue can be used to
create pretty much every colour sensation.

A fine explanation of colour vision can be found in `The Feynman
Lectures on Physics', by Richard Feynman, of which every self-respecting
library should have at least one copy.

Regards,
Ralph Savelsberg