From what Minmay said here and DJ Gopher said privately, I made some adjustments. The biggest change is in the middle-distance. I darkened the ground to ensure it's value stayed between the mountains and the fore-ground. I also added a subtle blue tint to the top edge. This helps define it on red gradients. The distant trees were too well defined in comparison to the ground they stood on. The trees now get more transparent as they get further away. In the foreground I altered the grass a bit to make each section less distinct. It's harder to pick out repetition now. (wasn't noticeable in the sample images) I didn't alter the highlights on collision tiles yet. I'm not sure if I want to.
If you're dying to get your hands on this tileset then you're in luck. I've discussed it with DJ Gopher and he says I may release all the tilesets I've made immediately. The others still need work. I'll be making a similar desert set in the near future.
Below is a before and after comparison with before over after, and the tileset.
Edit: The clouds are lame generic clouds. DJ Gopher didn't like my cloud concept, so I threw those in. Any suggestions?
Edit: Removed the old version of the tileset. Get the current version below