I would like you to use less colors for that Zero, you got a bunch of unnecessary red in there.
To many of shades can make the sprite look bad.
It would seem that you only need 4 reds.
3 blues
3 grays
and 3 skin colors.
ONce I have time I'll reduce your color usage and you can see what I mean. :3I didn't spend much time on it, just enough where you can see where I was going with this.