You really need to work on that palette, too. Try cutting it down to four colors for each main color (so four greys and four greens, then a couple yellows and reds for the details). Then And try to get a bit more contrast in there instead of having a ramp of straight grey highlights.
Also, the dark grey outlines are doing a lot more harm than good. If you're trying to antialias, you need to use it sparingly, and if not it just makes the whole thing look a little blurry.