The same gray looks completely different depending on what surrounds it
Josef Albers spent decades showing students the same phenomenon and they were startled every time. The eye doesn't read color — it reads relationship.
Place a square of medium gray on a white ground and it will appear dark. Move the same square onto black and it brightens. The pigment hasn't changed. The eye has changed its mind.
Josef Albers spent more than forty years at Yale and the Bauhaus demonstrating what he called simultaneous contrast — the way adjacent colors alter each other's apparent value, temperature, and saturation. His 1963 book Interaction of Color was structured as a sequence of visual experiments rather than a theory text. The idea was that you couldn't learn this by reading. You had to look, and then look again when the context shifted.
What Albers kept insisting is something that still resists common sense: color is never absolute. There is no such thing as a red that is simply red — only a red in relation to what is next to it. Painters had understood this intuitively for centuries, but Albers turned it into a teachable exercise. He wanted students to spend long stretches looking at two adjacent colors until they could see them shift.
The practical implication reaches beyond painting. Any judgment made in isolation — a number, a word, an idea — is as context-dependent as a square of gray. Change what surrounds it and you change what it seems to be.