Pink or green or nothing at all?
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 centre the moving dot turns to green.
Now, really concentrate on the black + in the centre 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. Of course there really is no green dot, and the pink ones really don't disappear.