IMHO this is the best optical illusion ever. The squares marked A and B are the same shade of gray, yet they appear different. This isn’t a joke! It is for real.
If you don believe us you can test it: just save the photo, load it in Photoshop and roll the color picker over A square and B square. So, what do you say now?
If you still don’t believe your eyes then in Photoshop join the squares marked A and B with two vertical stripes of the same shade of gray. Now it becomes obvious that both squares are the same color.
It is still hard to believe (I know it is)? Just hide in Photoshop the surrounding squares with a black color.
Now I think is all clear. Never trust to your eyes …