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 only a single green dot rotating.
It's amazing how our brain works. There really is no green dot, and the pink ones really don't disappear. This should be proof enough, we don't always see what we think we see.
The opposite color of red is green. Your eye sees the "after image" or red and the gray neutralizes the red (or pink).