Color is the most relative medium in art. In twelve rounds, your eyes will be lied to. See through the lie.
Two squares sit on two grounds. Are they the same color, or different? The grounds will try to fool you.
One square in the field is identical to the reference. The rest are impostors, dressed by their backgrounds.
Tune your square until it truly matches the target — ignoring what the grounds want you to see.
After Josef Albers, Interaction of Color (1963)