If your eyes follow the movement of the rotating pink dot, you will only see one color, pink.
If you stare at the black + in the center, the moving dot turns to green.
Now, concentrate on the black + in the center of the picture. After a short period of time, all the pink dots will slowly disappear, and you will only see a green dot rotating if you're lucky!
It's amazing how our brain works. There really is no green dot, and the pink ones really don't disappear.
http://www.patmedia.net/marklevinson/cool/image.gif
