... To be honest, it looks like some strange liquid splashed on the hair ( Also, the choice of colors burns my eyes D: ).
For now, you can go to tutorials section and watch some tutorials about how to draw heads. It should help you a lot.
Here is a list of all the tutorials.
Actually I am going to make some tutorials too... but that would take some time.
Oh, almost forgot, you also can watch how others have done the hair and then try to copy their style. i.e. watch some heads in
here and try to copy their hair. ALSO, I'd suggest you not to try selling them(If they're too similar, you easily can be infracted/banned for plagiarism) just try it for learning purpouses.