It's a nice start, and it works very well, but why don't you try some AA on this one. You go from black to pure white in one step, the ideal moment to try out some AA. Look at the grays you have first. Does it need another shade? Can you create a cool ramp out of your current colors?
Create that gray ramp, and look at how you can utilize it to AA the piece. It's not much work, but it'll make this piece double as good, and help your overal progression as a pixel artist...
It probably could use some more shades, especially on the wings, but I don't really even want to think about attempting to make the wings or the tail look more realistic, it would just take up way too much of my time.
I could probably create a ramp out of the greys, as far as it being cool... lol probably not.
I'm not even going to pretend like I know much about AA... infact I couldn't describe AA very well to anyone without looking it up first. Pretty much all I know about it is that it is used to make things look smoother.
So here's my quick edit to smooth out the transition from black to white:
It's not really much, but it is a bit more pleasing to the eye, also shortened the back of the cap.
