TypeLight and color
InteractiveYes: sliders and a check
First described2001
The inside of the shape looks faintly tinted. It is pure white.
Try this
- Tick Remove the inner line: the tint disappears.
- Change Inner line color to tint the shape any color you like.
Why it happens
Baingio Pinna, Gavin Brelstaff and Lothar Spillmann described it in 2001. The color of the thin inner line spreads across the whole area it encloses, and the shape also tends to look like a figure standing out from the background. It suggests the brain fills in surfaces from their boundaries, the same idea behind the Cornsweet illusion.
Did you know?
Map makers have long used a thin colored line inside borders to make regions look shaded without filling them.
References
- Pinna B., Brelstaff G., Spillmann L. (2001). Surface color from boundaries: a new ‘watercolor’ illusion. Vision Research, 41, 2669-2676. doi:10.1016/s0042-6989(01)00105-5
- Background on Wikipedia
The illusion on this page is drawn by code written for this site. Last checked 1 November 2026.
Frequently asked questions
Is the inside of the shape colored?
No, it is white. The color spreads from the thin inner line.
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