I see the tower on a chessboard as more of an illustration than an illusion, the point being that we don't really observe absolute colour because it's not terri

I see the tower on a chessboard as more of an illustration than an illusion, the point being that we don't really observe absolute colour because it's not terribly useful for making sense of space (which is what sight is for). The dress is sort of a variation on the same theme, except it divides people by how they extrapolate the rest of the scene.