I'm also not liking the leaves hanging down very much. They're a cool idea, but they don't match the large, wider leaf shapes you've drawn at the top of the tree.
The blue and purple are rather abrupt, they don't feel like part of the same ramp, because your dark greens have approximately the same hue (very firmly in the green range), while the blue jumps abruptly into blue and the purple is very abruptly purple. The purple being so light also doesn't really make sense because it looks like you have a secondary light source that's emitting purple light, rather than as a shadow that just happens to look purple in contrast to the yellow sunlight.
Try to break up the silhouette of the tree. Right now it looks like some very smooth balls with leaf-texture painted on them. Try having the leaves actually stick out of the tree. Here's a rough pixel-over to show what I mean:
(I also made your two darker greens bluer for a smoother transition and made the blue darker, and got rid of the purple bit.)