Optical Illusion

I spotted This at Beware of Geeks and it intrigued me. I love a good optical illusion.

Apparently squares A and B are the same colour. It's just your perception of the shadow that makes them look different.

Him who would warn us of geeks did a cut and paste of the two squares to compare them. Surely enough he came up with this:

They are the same.
Being a curious type, I decided not to take that picture at it's face value and I went a step further.

Watch this

I love a good optical illusion