If your eyes follow the movement of the rotating pink dot, you will only see the dots in pink color.
If you stare at the black plus sign (+) in the center, the moving dot will be ‘seen’ to be green in color.
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.