I've had time out recently, time to think and here's my thought to occupy you over the holidays. Why are there only three primary colours? Who decided that we should be restricted to this number. I mean BLUE, RED and YELLOW have been around for some time and I should have thought that someone would have found another by now. Just trying to imagine another colour that could not be manufactured by mixing any of the existing pigments excluding white hurts after a while. To be sure the three we have are pretty adequate but just imagine the scope we would have if there was suddenly another one. What would that colour look like? What colours we could mix with it!! I'm sure that somewhere on this planet there must be a mineral or a chemical of a totally different colour than anything we know of. We would have to re learn colour theory and obviously colour mixing would be all together different. I'm now going to continue thinking, after I've had another Whisky! Merry Christmas everyone!
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As a biologist as well as a painter, I think the rainbow is a good thing to remember. Colour is white light with certain wavelengths removed or absorbed, and our eyes have developed using the available wavelengths in the visible spectrum. I love your optimistic imaginative wish for a 'new colour', but I also love the way that all the paint pigments we do have can interact to create such lovely secondary and tertiary colours when mixed.

Thanks Alan, rainbows are full of beautiful colours, but I wanted another colour that was not mixable from the Red, Yellow and Blue primaries that we know so well. Most of the rainbow colours apart from Red, Yellow and Blue we can approximate by mixing the three available colours. Can't imagine it yet but you never know.

Have a look at a rainbow. All the available colours are already there.