I said that unnatural is not bad. Didn't you read what I said?
I THINK this piece could be improved by changing the colors. Color is relative, and when there is nothing to compare the contrast of that rich, vibrant green, to neutralize it, in other words, it is somewhat annoying.
I did a simple color edit to show you what I mean. It's okay to be unnatural, but you must know what you're doing first, so that it looks right! I hope that you understand what I mean now. By all means, continue using the same colors if you wish, I am just trying to help you understand a little bit about color... or what I know of it anyway.
edit: the green i chose is a bit yellow, making the yellow highlights kind of nonexistent. to fix that problem, just pick a green a little less yellowy.