B Robson wrote:
> Jean-Marc Desperrier wrote:
>> Brandon Berg wrote:
>>> "Brett Robson" <deep_m_m@hotmail.com> wrote in message 
>>>> I'll give you a hint, there are only 3 primary colours.
>>>
>>> I'll return the favor: I know that. Is your argument, then, that 
>>> color is a useless concept because not every color is a primary color?
>>
>> You're both wrong.
>>
>> This is not because the eyes of the human species are only receptive 
>> to three separate wavelength (as well as having seperate wide-spectrum 
>> receptors that enable to perceive the "luminosity") that this limited 
>> perception fully reflects the reality of things.
> 
> English isn't your first language is it? Try posting in your native 
> language, I think I'd have a better chance of understanding you.

My lack of command of the english language was probably a part of the 
problem.

One can say a color can always be decomposed into the 3 primary colors 
when talking about the restricted human perception of color, but not if 
you consider the nature of light fully.

http://www.fact-index.com/c/co/color.html

"Electromagnetic radiation is a mixture of radiation of different 
wavelengths and intensities. When this radiation has a wavelength inside 
the human visibility range (approximately from 380 nm to 740 nm), that 
radiation is called light. The light's spectrum records each 
wavelength's intensity. The full spectrum of the incoming radiation from 
an object determines the visual appearance of that object, including its 
perceived color. As we will see, there are many more spectra than color 
sensations; in fact one may formally define a color to be the class of 
all those spectra which give rise to the same color sensation."

And in fact even if we equate "color" with "human perceived color", the 
three primary color can only generate the color inside a maxwell 
triangle that can never cover the full spectral locus (the spectral 
locus is not a triangle).

See this for a complete explanation and illustration :
http://www.cs.bham.ac.uk/~mer/colour/cie.html