Contributed by Michael H. Brill, Datacolor
Here’s an illusion published by B. F. Skinner . Just stare through a pinhole at a tangent point (where two circles meet) in the pattern below, and the circles will take on various pastel colors. Viewing distance should be about 18 inches. No preconditioning by a "Skinner box" is required. By the way, I can see colors without using a pinhole.
What colors do you see? Can you find a presentation that accentuates the colors? Any explanation for the effect? Please post your thoughts.
 B. F. Skinner, A paradoxical color effect. Journal of General Psychology 1932; 7:481-82.