I think right now, it's pretty much about polish. The lines are solid. (
just realized they aren't your lines. ) just keep playing with the colors and try different dithering styles. Add some more hues, for example, instead of using the same hue in the darker green, make it more bluish, and then add another color inbetween the blue-green and midtone green...
Also, with a dragons skin, the scales could be taken into consideration for the dithering, you can use the 'style-dither' method, where instad of just using 2x2 meshing, you add in random 2x2 blocks, or 4x4 circles.