Wow! thanks for all the great comments!
I'm posting to say that I've touched it up a bit, so now it is finished

I erased a lot of the coloring until it stopped coming out of the lines, I made the earth dragons eyes a tiny bit greener, I gave the grass in front of the feet more definition, I made the dragons cast shodows on the grass, and I put more sunlight in the background to make the dark dragon stand out.