This (and Pre-Schooler) can be obtained as early as level 2-2. At the beginning of the level you will get the Tricolor Chromagun. Shoot any wall in the room that you get the gun in with any 2 colors to get Pre-Schooler, then just walk into the next room, turn left, shoot all 3 colors at the droid and then shoot any color that you've already shot at it again and you should get Doing it Wrong.