That's a pretty good drawing, when coloring I usually think about 3 things Shape, Edges and Color
For shape your piece simply doesn't have a clear light source. Try simplifying the lighting into 3 shapes: Light Shapes, Shadow Shapes and Mid-tone Shapes. If you map these out before going into things like edges, texture or even color, you will have an easier time applying them or adding other lighting sources.
For edges I like to simplify it to hard, firm, soft and lost edges. looking at your piece, the face in particular has only one edge on it, a soft edge going up and down the face. The edge should instead be a hard edge to indicate that it is a hard shadow and the nose should also have a firm/hard shadow to indicate the bottom plane of the nose. Getting good edge control is mostly down to painting more and observing from real life where those 4 edges I mentioned tend to occur.
For color I usually try to strike a good balance of warm and cool tones. In your piece the warm and cool tones are mostly balanced aside from the all the black present. I think you can solve this "being forced into using black" issue by painting over the sketch instead of under it. If you need the sketch as a guide you should at least lower the opacity of the layer as having dark lines tends to skew your sense of color and leads to the issue you describe. If you want the sketch to show through in the final result, it should be clean enough that almost all the lines in the sketch has a reason to be there, take the lower left hair for example, the lines feel unconfident and I don't really know what the lines are trying to convey. A good check for this is to look at your line and ask your self "What EXACTLY is that line for?" If you can't answer in less than 5 seconds or you have a very none specific answer, then that line needs to be redone or removed.
I hope this helps, you should also look into Marco Bucci's 10 Minutes to better painting series, especially the video about shape and edges.
https://www.youtube.com/watch?v=nnhj5efzN_w
https://www.youtube.com/watch?v=-ZknWKTpc90
I am excited to see how you improve and good luck!