It's a good idea to really think about what kind of background your sprite is going to be on, too. If this wagon is supposed to be out on a sunny day, the colors are very sickly and weak looking. If it's supposed to be out during a thunderstorm, then they might be alright. You drew it on a dark background, so I'm kind of assuming it's made for a darker area, but figured I'd throw it out there, just in case.