Optical Illusion

The human eye (and brain) perceives an object's color not based on its actual color, but on how it compares to the surrounding colors.

In the large image below, the "brown" color in the middle of the top panel is exactly the same color as the "yellow" color in the middle of the lower left panel.

Don't believe me? Drag the small brown color patch below to the 2 spots and see.