Hey belM
'Colour' is just the sum of wavelengths of light entering your eye. If you have a source of light (something that produces it) then the more wavelengths represented (the more 'colours' you add) the closer the experience will be to white light.
Objects that you see on a day to day basis (apart from light bulbs) work by reflecting a certain wavelength of light at you. The reason they do this is because, essentially, they absorb all other wavelengths. This is something that our teachers in school never made very clear - an object appears to have a colour because it absorbs all other colours, so the only light reflected off it is what's left. If you think about it this way, it becomes simpler to understand why, if you mix pigments, each of which absorbs all but one colour, you will eventually end up with an amorphous blend that absorbs most light and reflects small portions from various patches in the spectrum - hence a dull brownish-grey as your final result.
tsuwm, of course, explained all this a great deal more concisely, but I just couldn't resist.
cheer
the sunshine warrior
