I did a quick edit:

The farthest i could get the color count down to was 22. In yours, the eyes and the shade that sorrounds the left eye (his right) takes up 2 colors. If you make the eyes the same color as the darkest shade of the skin, that should take down a color. Also, in the mustache there is a color that you only used with 3 pixels. You can take that color out and it doesn't really make a difference. Also, Maybe add some backlighting (I think its called that) on the crown, and the robe.
I'm very bad at explaining things but i hope my edit helps.