Yop, really nice work Moogie.
You should start to change the background. You\'ll see it will affect a lot your perception of colors. (use a grey background for example).
Instead of color burn (which will destroy too much colors) you should use multiply mode. It will darken too but more constantly. Color dodge is good, but not on too big surface, it\'s perfect for small highlight.
You can use screen mode to light up. Just try to use the color you want to light with it. (example: use dark red in screen mode to light up a red color).
After everything depend of what you want. You can use the smudge tool, which is pretty powerful, or just use a rougher brushes, to have something harder.
A good techniques is to start making shadows and highlights and then you go back to a normal mode of blending at 50% opacity and you paint picking colors on your drawing.
