http://en.wikipedia.org/wiki/Same_color_illusion
The same color illusion—also known as Adelson's checker shadow illusion, checker shadow illusion and checker shadow—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. The optical illusion is that the area of the image labelled A appears to be a darker color than the area of the image labelled B. However, they are actually exactly the same color.

You can drag the bar at the left and move on top of A and B (or click auto checkbox).
You can also drag the slider to change the color of the bar.

You can hide other blocks if you drag the second slider to highest value.

Those two orange dots are the same color. try to drag one of them to block A, another to block B.
Are they look the same color after being moved?
Enjoy the fun of illusion! Trick your mind! ;D

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