LOL, whoops! I didn't realize about the lineart, ahaha, my bad. *Smiles*
You can also adjust the gamma, levels..play around with that. One good thing to do is to find a reference picture. You can take off the colors from a picture to make it more natural, and you'll learn a lot more about realistic colors.
Something that needs to be considered is that light itself is actually white, and the amount of light will determine the value and saturation of any color. For example, holding a flashlight up to your finger will make it a lot redder compared to standing in direct midday sunlight. Be sure to also play with the balance of the shadows in terms of transitioning and reflective light. (The reflective light should be no darker than your darkest tone of your light colors.)
The skin, as it appears there, is yellower, and it makes her seem sallow and unhealthy. Skin can contain a wide variety of colors, from oranges, pinks, blues, purples, and even greens.
Color burning can be great, but it's better to learn to SEE the colors with your eyes. When you start a picture, find a reference, and start making a pallete. You might even drag, say, a pink hue over the main tone at a low opacity to get the desired color. Don't let filters determine your colors; it can loose a lot of reality by doing so.
Practice, practice, practice!
I personally tend to use a lot of clipping masks and I use a hard brush with a low opacity and flow. Then I give the hardbrush a bit of softness and go over it with, once again, a low opacity until it blends in. This makes your lines crisper.
You can use another layer to do stuff like that, but just try bumping up the contrast if it's not enough in the end. Just be careful not to "blast things to black."
Secondly, remember that blacks aren't always truly black. If you try to mix black yourself, say, with paint, you'll always end up with a slightly tinted hue.
Take the time to view some tuts on Youtube, or just watch other artists. Practice from RL. If you need any help, or tutorials, lemme know. http://www.youtube.com/watch?v=jp9wGrSVP7U