Admit it, most (beginner) artists would take 50% of their time to fix the hair of their drawing. It happened with me, and happened to almost students in my class during my college. It still happened to me until now when I even only take a coloring project.
So, is drawing hair really difficult? Well, actually not. But most of us are loving details and want it look perfect. Actually, as long as you know how it works - I mean - the trick to draw hair, you wouldn't occupy most of your time with hair.
The followings are drawing and coloring hair tutorial. Especially for coloring, either you work traditionally or digitally, the principles are same: you will always start with the softest color of the hair, and later choose areas for darken and darkest.
Hope that the tutorials here can help you! One more time I take Red Priest Usada's work. And for the first time from Teagan White -- deviantart's artists. Also, visit their page to see their latest work!
Drawing hair tutorial page: here
Coloring hair tutorial page: here
*) When you want to download at Deviantart page, look at the left side and find 'Download' link. There, click it to get the file. Or.. use right click and 'Save as'.