I use a lot of layered effects for the syth skin, I first airbrush the dark colours (in this case dark black with a hint of blue, three airbrush layers with more light blue/grey added)
I then do a technique similar to dry brushing, but instead of a back and forth motion, I use a flat wide brush in a "stabbing" or stippling motion so that I can better control where the paint lands and only hit the higher up bits.
After that I us a watered down home made wash to blend it a bit, followed by another round of stippling, followed by another was and then selectively hitting the highest points once or twice.