After you do the Super Sonic code, (Sonic 2-Super Sonic {Real Way} Cheat), collect 50 rings and jump, (before you do this, use the Sonic 2-Debug Mode cheat), press Start, and tap B repeatedly. You should see Sonic changing colors.

Note #1: Sonic changes in this order: pink, blue, then yellow.
Note #2: If your timing is right, Sonic's colors will change to white on the front and black on the back (before he turns pink in note #1).