Optical illusion: By land or by sea?
This optical illusion, devised by psychologist Richard Wiseman of the University of Hertfordshire in England and created by software developer Matthew Wilkes, makes a map of the world appear more differentiated than it actually is. In reality, the "green" stripes through the landmasses and the "blue" stripes in bodies of water are the same color—the brain perceives them as being different colors based on the intervening contrasting stripes, which do in fact vary from orange to purple.* (For confirmation, check out a small section—the southern tip of India and Sri Lanka—enlarged to show detail.)
*Clarification (7/8/09): This sentence was edited after publication in response to reader comments.