Hi, I must say I really really love the alien world feel you have captured here, the colors are spot on for your theme choice, great atmosphere. Well done.
I also love the additions from Schwee.
I would agree with MysteryMeat in that your middle ground is too flat/void of detail. I fiddled with it a tiny bit but I really strongly think if you allow yourself a few more colors you could really go wild with this.
I stuck to your colors, so getting the depth of middle ground was tricky and perhaps might not look right, with even 2 or 3 new colors introduced you could really improve things, or even more colors! I love color! heh
Just another thing I notice, which I see people often do, is, generally speaking, (not always) terrain/features on landscapes going far into the distance tend to get lighter not darker. Intuitively you might think the other way around though. Mostly dude to atmosphere, slight haze.

Don't give up on this yet I would say... Keep up the good work.