These are really nice looking. The ships look "right", for the Star Wars universe. As far as color, the work you're doing is very good, but maybe you should try putting flat color (Use the multiply level in Photoshop) over the rendered pencill drawings. It will give you a new look that you might like. Aslo, when coloring on the computer, always put a bit of the complimentary color into your chosen color. It will help the colors feel richer and and more earthy. For instance, if you choose a blue on the color slider, put in just a tiny bit (maybe 5%) of yellow and red. If it helps, try working in CMYK, as opposed to RGB. CMYK is more like mixing real paint.
It would be cool to see you color one of the ships!
Hope you don't mind the tips!---Mike