The Colours You're Forbidden

Your eye has only three colour sensors, and every shade you have ever seen is mixed from those three. But the wiring lays down rules. Red and green are opponents, wired to cancel; blue and yellow the same. You can see a yellowish-green or a bluish-red, but never a reddish-green or a yellowish-blue — the system is built to forbid them, the way a switch can't be both up and down.

And yet they can be smuggled in. Stare at a fine boundary between red and green until the sensors fatigue, and people report something they cannot name — a colour that should not exist, both red and green at once, flickering in a brain briefly tricked past its own rules.

Beyond us, the limits look almost cruel. The mantis shrimp carries not three sensors but a dozen. Birds see ultraviolet, and the plain flower on your table is, to them, painted with landing lights you will never witness. The rainbow you call complete is a narrow slice, cut to the shape of human hardware.

And if your colours are just three sensors and a rulebook — how much of the world is simply off your menu?