Her skin tone needs to be brown, but it also needs to contrast with her outfit, and it can't be too dark or you won't notice details.
I might suggest looking for pics of Halle Berry when she played Storm in the first X-men movie, then I would lightly use the clone brush over the facial features and use those pictures as a way of cloning in the appropriate skin tone. I wouldn't use one particular photo, instead I would look at several different photos in different lighting, because lighting can drastically effect color.
http://i219.photobucket.com/albums/cc155/shinsupremekai2002/X Men/storm22.jpg
Also her breasts aren't shaded quite-right.
You'll want to look at this tutorial on properly shading spheres.
The same principles can be applied to digital painting.
http://www.ehow.com/how_2097618_draw-shade-spheres.html
Hair:
I would suggest keep it dark, even paint it a little darker,
Paint in layers, layer on darker shades of gray followed by lighter shades of gray then strands of off white and a few highlights to keep the hair looking natural. I would use the hair in this photo as a paint by numbers example to use.
http://3.bp.blogspot.com/_vdw4wiD3TGE/S8IHm0HDXgI/AAAAAAAAADA/--kaCnJAShI/s320/Storm_xmen.jpg
Black Leather:
Black leather is difficult because it requires the same shading values as metal with a lighter touch of the brush, and is also defined by longer, softer areas of highlight, but it also requires it's dark values in the shadows to be truly believable, it also requires a lot of blended tones, and softly blended light to dark values between highlight and shadow.
I would look at pictures from The Matrix, many characters were wearing long leather trenchcoats and leather armor, which if you looked carefully at the shading and compared it with your picture you'd understand why your colorations are off and where the problem spots are.
It might also be a great idea to pause here and save a backup for a possible future Jean Grey skin.