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.

There are two baffling color illusions demonstrated below:

• The color squares behind A and B are identical
  
  Don't believe me? Drag the small gray color patch below to the A and B areas and see.

• Another Optical Illusion example:
  The checker shadow illusion is an optical illusion published by Edward H. Adelson, Professor of Vision Science at MIT in 1995. The image depicts a checkerboard with light and dark squares, partly shadowed by another object. The optical illusion is that the area labeled A appears to be a darker color than the area labeled B. However, they are of identical color.
  
  Don't believe me? Drag the small gray color patch below to the 2 spots and see.