Stare at the black cross in the middle. You'll see the blank spot after the dots move turn green....29 Optical Illusions That Will Seriously Mess With Your Mind 14 - https://www.facebook.com/diplyofficial
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 see only a single green dot rotating.