6. La Raie changeante

It is, then, one of the inherent qualities of our medium that, if I have a green stripe divide my drawing in half, the stripe needn’t be green to you.  This is why we can’t have green as an individual colour.

But Henri Matisse doesn’t just have the green stripe—he composes Madame Matisse in portrait around it, painting the two halves of the face two different colours.  If I, like him, have two different colours—something green to the left, say, and something less green to the right—then, no matter what the two colours are to you individually (which would depend on the device you use), the right would be less green than the left to you too, the left green next to the right.  And this is how we can still have green—not as an individual colour, but as a relationship between colours.

Not as an absolute colour, but as a relative colour.