I think you should explore "bitmap" colors, instead of "vector" colors ...when I say bitmap, I mean something that isn't linear - something that allow for some grit, dirt, splashes - in short, something that will bring your vectors to life, instead of a "linear" coloring ... not sure if I express my thoughts very well, so I mocked up a very quick example :
http://www.luxgames.net/FK/tanky2.jpg
Of course, it all boils down to the style you wanna give to your image, my point, is : don't limit yourself to a "vectorial" coloring, eventhough your outlines are vectors ...actually, the clash of two technologies can create something quite interesting
