Yeah, a little bit too many colors, but the reason for this is simple - i wanted it to be as smooth as possible :) I wouldnt be consequent if i would dither or something.
This is also cool. You can actually get nearly the same results though with half that number of colors. Try removing some of the unneeded colors in the sky and the outline of the truck door. You have some colors, like between the front and back of the truck, that are each only used on a single pixel.
it's cool