The chums over at Brick Fanatics have found two new characters that will be in LEGO Batman 3: Beyond Gotham. Amazon UK has a Rainbow Character Pack DLC to go along with their pre-orders of the game. The Rainbow Character Pack includes playable versions of Rainbow Batman and Rainbow Raider.
Rainbow Batman first appeared in Detective Comics #241 and Rainbow Raider first appeared in Flash #286. These two characters can probably be unlocked in the game as you play through it.