No you get me all wrong, you only use hue shifting for small differences. Instead of making bigger shifts you usually add a back light in a different color, often blue, cyan or magenta.

Take a look of the very well known tree of "Secret of Mana 3".

It uses a shift from green to blue, yes. But only in a small range. Less than the half of what you were recommending. It also uses magenta back light.

But now take a look at the other palettes used in the visible part (the first is the dirt, the second the grass and the third the rock), they all shift in the opposite direction. So the tree is more the exception than the rule.

The question is now why did they do that. I think once because they wanted a bit colder atmosphere and second to have better contrast between the background and the tree.

Sorry, but that looks just plain horrible. I don't get what problem you are trying to solve.

The only problem I currently see with my version is that it looks really repetitive if tiled even though there are variations (There are two 32*16 tiles which can be combined arbitrarily.). But I think I can solve that by using less, bigger rocks so it's not recognized by the human eye just as a big complex mess.

The vegetation is for the oasis, so it's what is near water. (Just didn't do the water yet )

Only $13/hr? Wow. That seems to be a really low price to me. It makes me wonder even more because you are apparently a very experienced artist. From what I've read so far the usual wage for a professional pixel artist is between 20$ and 30$. How comes that you sell your time that cheap?