Colours

[cbmvax!uunet!gandalf.otago.ac.nz!CHandley]

Hi,
Hope this gets thru, I am testing my access to the discussion and my 
new mailer.

I have been reading most of the discussions about a variety of 
topics with great interest, but have not had time to respond -  
actually I still don't, but what the heck, I could not let the 
discussion about colours go un-answered.

The 3-colour theory of colour production, whether with paints or 
with lights (filters, phosphors or whatever) admits that you cannot 
produce all colours that way, a fact that is usually conveniently 
forgotten. If one looks at the colour space produced by the CIE, one 
can see that it looks something like a parabola lying on its side. 
Using three colours one can only produce the colours within a 
triangle. Thus, even if one used spectrally pure green, red and blue 
(whatever that may mean), one could not produce the other spectrum 
colours, nor the psuedo spectral colours along the purple line.

This then raises the question of how many colours there are along 
the spectrum and how do you name them. That I cannot answer - 
'English' recognises 7, other languages/cultures undoubtedly 
recognise a different number. At a bare minimum however, from a 
purely practical point of view, we need separate names for the three 
primaries (red, green, blue), the three secondaries (cyan, magenta, 
yellow) and the two mixtures (black and white). What you do about 
the rest comes down to theology, in the same way as naming the 
elements - what are recognised as distinct and what are useful for 
every day conversations.

Chris.
(My employer couldn't give a damn what I say)