Thank you, I understand what you mean. But it's hard to fit such things into 16 colors.
Very cool style and palette!
My only issue with this piece is the lack of "contrast of details" / center of attention (not sure if you see what I mean).
My gaze is having a little trouble knowing what to look at. This is why it's usually recommended to not use the same level of details in the background/foreground than the "center piece" to highlight what you want. Or just to use more contrasted colors on each different plan.
Here a very rough example of what I mean, with the attention focused on the rocks/tree.
Beautiful! Not quite Bilibins style, there's a bit more volume/thickness, but I don't mind that one bit.
This is absolutely gorgeous. So many beautiful colors that complement one another so well. I can tell a lot of thought was put into this. I love the yellow highlights and the purple grays of the trees. Also the contrast is so appealing. I really like the design of the frame and the rocks too. Great job. 
Yeah, that's true, but you have a lot of different "contrast" methods you can play with that are not directly related to the color count.
It can be contrast of details (less details in the background, so it's more readable), contrast of sharpness (not easy to do in pixel art, but basically trying to render something like if it was out of focus / blurry), contrast of saturation (not sure you have enough colors for that here)...