Optical Illusion

http://www.johnsadowski.com/big_spanish_castle.html

This is an interesting one. The picture is in black and white.

Move the mouse from the picture and you will see the negative of the picture.

Stare at the dot on the negative for 30 seconds and then, still looking at the picture, move the mouse back over the picture. You will see the picture in colour until you move your eyes.