I have to say, as someone who struggles to do any shading at all (I just can't seem to get the hang of it, frustratingly), this is very nicely done. Congratulations. However, the thick, black lines in the folds of her dress seem to be only marking where folds in the cloth are, and most of the dress is the same shade of blue, making it difficult to pin down where the light is coming from. Personally, I am still learning how to accurately draw folds in cloth, so even though the shading is off, I know that where they are placed and how, is very well done too. Perspective is another troublemaker.
As for your colors, they work very well together, and even with the lighter colors, it still is a very somber piece. I can't really find any problems with your coloring, except for the shading issues mentioned above.
The only other issue I can find, would be the girl's design. It was probably unintentional, but she appears to have a rather long, er, behind. I didn't notice myself until I had looked at the picture a couple of times. Even if her belt is higher than her waist, it still is rather awkward.
Overall, a very nice piece, but with some room for improvement. Well done!