Illusion of the Week

Notice the grid of black, white and two shades of blue. Would you believe that all the blue is precisely the same shade of blue, instead of there being some light blue bars and some dark blue bars? There are endless variations of this color contrast illusion, which is sometimes called the Munker-White Illusion and sometimes the Bezold Effect. When the shades involved are black, white and grey the same illusion is called White's Illusion.

All of the small bars within each pattern are actually the same color (i.e., all of the blue segments are the same color blue, all of the red segments are the same color red, and all of the small grey bars are the same color grey). The lightness differences you are experiencing are massive illusions. A theory of what's underlying the lightness illusions in this figure is described in a paper to appear in as special issue of Perception on "Contextual effects on color appearance."