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.
It's amazing how our brain works. There really is no green dot,
and the pink ones really don't disappear. We don't always see what
we think we see.