If your eyes follow the movement of the rotating Pink dot, the dots will remain only one color...Pink.
However 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, all the Pink dots will slowly disappear and you will only see a single Green dot rotating. It's amazing how our brain works for there really is no Green dot and the Pink ones really don't disappear.
Thanks to Sheri for this sample.