You can increase the contrast in the trees without your players thinking that they're part of the foreground. The main issue is between the tree and the leaves in front, and the background. They don't pop nearly enough. Distinguish your colours - maybe a colour wheel would help? - and it will look so much better.
The platforms should be the things that pop the most, so put a particular emphasis on making them stand out.
I mean, yeah, it's one thing to have dark, subdued colours as a theme. But when everything looks the exact same, it gets monotonous and boring, which is why you need to have a few elements contrasting to make them stand out.