The palette is a bit messy, there are a few colors you only use once or twice. You can or choose to use 'm everywhere, or choose to delete 'm. I did a combination of both, and tried to overdo everything.
I started with this because I thought you used a too bright color on the top of the head. if you would have done it a bit less bright, you could have used another color for highlights, but keep the amount of highlights little.
Anyway, I started putting in more dark and bright areas, edited your palette a lot, and got here.
yours >>>> mine
Oops, somehow the transparancy got lost!? creatively
fixed!