
Your rocks are so dark i can hardly see them. :/
palette wise -> im not sure you are thinking about how light hits rock surfaces when coloring. all of your values are in the same area of hue, which would indicate that your light source is of the same nature as the twilight ambiance, Ive thrown in some values that are far less saturated and closer to the yellow hue range for the highlight regions, and let that progress towards your blue/greens as the values become darker. It allows you to keep your strong blue hue influences without sacrificing the natural hue of the object being lit.
Also, i would suggest to pay attention more to the light source angle and how it fills out the shape of the stones before worrying at all about the very indepth amount of anti-aliasing youve got going on (which makes it look impressively smooth). I fall prey to this often, but step back and figure out the shapes before going nuts with the detail. For the face/rock thing on the top in particular ive tried to push the highlights so that they hit more topdown from lets say a moon light source rather than what looks like a spotlight angle that looks like it might be flattening out your forms a little.
also remember rocks have sharp edges, and the harder you hit that highlight the sharper itll look. also remember if there is a sharp edge, that whole face of rock is probably nearly equally as light, or else it kills the illusion of its geometric faces. (aka rocks can be tricky

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One comment i had about your trees, why do they all slant in different directions?