Avoid "inner black outlines", ie black single-pixel lines that separate two colored areas of the sprite. They take up precious space, and very often they don't bring anything. If your character design allows it, the frontier between two colored areas should be enough.
In your case I'm pretty sure you can remove the lines around ear and between hair and neck.
Coloring dark outfit is tricky, one thing you can try is to shade the (top) front of the thigh lighter, since it is more perpendicular to a possible light source coming from top.