Eli5: How does the colour purple “not exist”?

Question

Eli5: How does the colour purple “not exist”?

In: Physics

Answer 1

What’s red and blue pigments combined?

Purple, right?

But what’s the wavelength halfway between red and blue?

Green.

So how does the brain distinguish between a combination of red and blue light, and the light halfway between red and blue?

By using a different set of pathways to recognize the half-and-half light differently than the in-between light.

The result is that the brain “sees” a hybrid color that can’t be represented as one single wavelength.