umm, your paper is not white. Its either that pic is scanned with a non whiteish paper, or you took a picture of it. If the drawing isnt drawn on white paper, it will complicate things, and would require extra steps, and would not look as nice as its suppose to look as, due to the color. The same as taking a picture, as lighting affects.
I can help you with your first few avatars, just to see if its on white paper/any other issues, so that we could say that it is the drawing at fault and not, the program. Pm, any questions and ill help out.
I use Fireworks btw.