h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is fascinating! Wittgenstein was greatly exercised by the question, as was Goethe, I think. Wittgenstein couldn't get over the fact that it seemed true to say "a thing cannot be both red and green all over" and yet it doesn't fit into normal logical exclusion.

The development of colour vision, the fact that we construct our spectrum from (is it?) green blue and yellow sensors of very different strength and greatly different antiquity, is a particular study in evolution.

Have you come across Friese-Green (yes! the Goons didn't invent the name) and his method of producing colour film from monochrome photography?

No, I haven't heard of Friese-Green.

Yes, colour vision is an interesting combination of physics (colour frequencies and so on) and perception (grey shadows appearing red etc).

Newton used a prism to split white light into different colours and based the normal theory of colour vision on his results. Around the same time, Goethe held the prism right up to his eye and observed that no matter what colour went into his eye, it looked white. Most people dismissed this as some literary guy dabbling in science he didn't understand, but he had a valid point - the perception of colour is based on contrast between one colour and another, not on frequency of light. The eye can detect the colour of an object independently of the frequency of the light coming from that object.

But there's a lot of work in it and I've put it on the back-burner for now.

I've seen a Friese-Green film on TV. He printed a film in one colour, red or green, and superimposed the negative in the other colour (I think that was the method) and when projected, all the other colours appeared. How did he think that up?

Goethe was a hundred years after Newton by the way.

Actually I've a vague memory of having read about the Friese-Green technique, although I never heard his name.