The line art and form has a wonderful elegance to it, but I think your shading should reflect this. Try messing around with colors for shadows and be aware of ambient lighting. Shadows aren't strictly black (sometimes maybe) and tend to reflect the environment around them. Experiment with colored lines as well. If you're line art is on another layer, use alpha lock to help yourself paint them in however you please. The wings look angelic and that really adds to the piece. Experiment further with brushes, especially for your background. Even using textured brushes in some cases can help with shading the color in line art. I can't wait to see what else you have to tell through drawing!