

Went ahead and gave it a 16 color palette instead of 19 (I think it was). I don't think gray is a color that should be used lots in video-game protagonists, but others might disagree. Anything from a slight tint to a whole secondary ramp (as I've done here) I think unifies the colors much better than 'green + gray parts'. It gives you the chance to suggest the hue of the lightsource as well as portray a more pleasing range of volumetrics, I think. I went ahead and added much contrast, cleaned the design a bit, changed things I thought would look better (strictly personal thing. I never would put the cannon of the vehicle
behind the cockpit, though that might have been the original idea for the NES sprite for all I know). I changed the wheels dramatically, which I think were the biggest fault. I made the protagonist sprite much simpler because I think the NES sprite had a certain charm that must be retained. The smaller the sprite generally, the less colors and detail there should be pushed in there.
I hope this helps. If you keep anything from my advice, make it 'more contrast, more distinct colors'.