purple. Are the neutrals on top or on the bottom?
Trompe L'oeil began ages ago in traditional oil painting. A famous painting was of a window frame and a boy climbing out of it. In more modern times it appeared in op art as artists began exploring visual perception vs. what was actually painted on the canvas. My "phase shift tribute to op art" plays the game of what color is on top and what color sinks to the bottom as the same colors change when they are put on different backgrounds. The repeat works as standard and half drop which furthers the illusion.