Looks incomplete my friend. I would work out your proportions before you start loading in color, and when coloring be sure to apply finer aspects of color theory to make some good shades. Instead of doing your darks with black, try green for your darkest areas and blue/purple for others. Layering the chalk then with red will create a very natural look.

If you're going for a graphic design aspect, still don't shade with black. Simply use it for lining.

Very cool! Excellent use of lighting. Is this digital?

I almost thought this was something from Overwatch, I've been too obsessed lately. Cool sketch!