If all you want to do with this game at the moment, is to change the hair color - then you might not need to change the sprite. I suggest the first thing to do, is look at the structure of a save state file of some Genesis emulator. Find out where everything is in that file (you might need to unpack it first). Find the palette data for the hair color, change it, and reload that save state into the game. See if it works. If so, you can go about looking for the palette data in the rom (which is a lot easier than tile/sprite data).