December 11, 2013 
Are these two blocks in the picture in different colors? Are you sure?
Although we encounter optical illusions daily on social networks, now and then some illusions become a viral hit.
So, what is it about…
Look at the picture. Are these two blocks in different colors?
Although most people consider that these two surfaces are in two different colors, the upper block is of the same color as the lower block, and middle part is what is causing the illusion.
The point becomes clearer when you look at the picture below and use your fingers to cover the central part.
This is a variation of the well-known Cornsweet illusion, and in this case it is the work of David Smith and Kottke.
Taken from: www.index.hr