Almost 2000 colors, i am pretty sure you can optimize it quite a lot. Otherwise, good job.
wouterpleizier.nl/pj/index.php?input=http%3A%2F%2Fpixeljoint.com%2Ffiles%2Ficons%2Ffull%2Fwhoyagonnacall2.png
This could help:
pixeljoint.com/forum/forum_posts.asp
It looks like majority of those colors are (dare I say, wastefully) used on the gradient effect. I'd argue you could easily cut down the background to use only 10 or so shades, much like the road under the car