The mountains look good, are they a brush? If I may make one small suggestion for you to try out, try adding a little green. you want a green that is roughly the same value and saturation as the dark browns, then try painting in green along the base and up along the slopes, not much just a little to give the impression of a treeline. Try it out and see what you get. Oh and another thing to try out is instead of using black make the black a very very dark blue, dark enough so it looks black but not quite. You have to expirament to get it just right. The blue will act as a cool color while the browns are warm it will bring the colors out more.

Keep up the good work.