The Mysteries of the Rainbow

I go through most days acting as if I understand colour. I dress myself, stop for red lights and go for green, I pick the brightest berries at the supermarket and point to the yellow tree and say, “It’s fall!” or “It’s dying,” depending on the season. But using and understanding are not the same thing. Humans have three colour receptors in their eyes. Mantis shrimp have twelve. Humans, so long as they’re not colour blind, can see somewhere on the order of a million different colours. And the shrimp? Red and yellow and green aren’t as important for them; their complex eyes are trained on the UV spectrum, on light that humans can’t see. So, do they see less colour than we do, or more? Do they see colour at all?

The ontological confusion of colour—what it is, where it is, and what matters about how we see it—is the point of departure for On Color, in which David Scott Kastan, a Shakespeare scholar, and Stephen Farthing, a painter, guide the reader along the...