They're coming from the tree's, man!

[Redwiz]

I've browsed a lot of the work around here and everyone is falling into the same pitfalls : Contrast. You've gotta be more confident with the jumps between colours.
Heres an example i hope you did not mind me editing! It's not neceassarily any better than yours but is mainly showing what contrast can do to bring it off the flat environment a bit more.