It's a repost from a very old thread
If your eyes follow the movement of the rotating pink dots, the dots will remain only one color, pink.
However if you stare at the black "+" in the center,
the "moving dot" changes to green.
Next, concentrate on the black "+" in the center of the picture.
After a short time (maybe a minute), all the pink dots will slowly disappear, and you will see only a single green dot orbiting around the plus sign.
It's amazing how the brain works. There really is no green dot, and the pink ones don't really disappear.
This should be proof enough, we don't always see what we think we see.