I've heard comments that there should be more colors, but honestly I think we have plenty to work with. 5 point gradient on browns, 4 point on red-yellows. White-cyan-blue works great for water and sky. Dark grey can even pass for dark green if juxtaposed against the two greens. Here's an image with some examples.
The beauty in this game is how simple the tools are vs how elegant of pictures that come out. Between creative color choice and erasing to shape non-circle brush strokes, there's a lot of room for creativity.
Thoughts? Examples of good panels?