Adelson's Checker Shadow

The poll on the colours of squares A and B is now closed, and as almost half of you guessed, the answer is that both squares are the exactly the same colour. From Wikipedia, 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 checker-board with light and dark squares. The optical illusion is that the area of the image labelled A appears to be a darker colour than the area of the image labelled B. However, they are actually exactly the same colour.