I suggest you read the tutorial on how to paint in OC before attempting this. So, please, get familiar with Derek the purple elephant first. And again... we don't need no stinkin' layers!
As with Derek, pay attention to the flow of your piece. With hair, you can have a lot of flow to deal with. Never go against the grain. Also remember that natural hair has many colors that make up a whole, so keep this in mind even though this is on fantasy hair color rather than natural hair colors. Running a little blue or lavender into that silver haired pretty boy's locks will make his hair feel more real.
Again, KNOW YOUR SAVE COMMAND! Ctrl+S. OC doesn't allow you to undo a whole lot of steps, so keep this in mind and save while you still like the piece. Especially so when doing fantasy hair, since you will likely have to experiment with many colors to find colors that compliment well and feel natural.
Meet Aura, my subject for this tutorial. Aura will not be available as a test subject as this is a more advanced tutorial than Derek and assumes you already have a basic grasp on the tools.
Oh shut up, this isn't how to draw anime, people. If you want that, you're in the wrong tutorial.
1: I used a brush size 3 for this, you can go a little larger if you want and use a 5, but I wouldn't recommend it unless you have a huge picture and need to do a whole lot of hair.
Use the base color application from the Derek tutorial and give the hair a good base color. If you're doing white, crystal, silver, or gray hair, you'll want to pick a darker base color than what you want for an end result. You can ease up the pressure a little where your highlights will fall and darken it a touch where the shadows will be.
At this point I wouldn't try to kill the "lines" in the hair here entirely, since it'll remind you of your flow and how the hair should fall.
Since Aura has more of the crystal/white type shading, leaning a bit more to the lavender spectrum, I've picked a sort of lavender pink as the base color.
2: Pick another color, darker this time. Run it lightly all over, and put a bit more where the hair should be shadowed, do it more sparingly where your highlights will be.
3:Pick a slightly lighter color than your base color, brush it all over, use it more heavily where your highlights will be.
4: Select the pen tool. Put it to 100 opacity and set the size to .5. Grab that first darker color you picked, stroke some of that into the work, again, more heavily where the shadows will be, lighter to none at all in the areas where the highlight goes. Through all the pen stages it's alright to let it overlap a little bit outside of your hair lines.
5: Pick a shade close to what you want the end result to be... run this lighter tone all over.
6: Pick another color, I'd suggest a warm one here. If you're doing natural color hair, this will be the golden tone that's normally found in hair. For Aura I used a soft candle flame gold, very sparingly. Put this around and in the areas where the highlight will go. This gives it the feeling of light reflecting off the hair. If the character isn't of a very friendly temperament or has truly jet black hair, you could use a dark steely gray or blue instead of a warmer tone. It's up to you.
7: Pick a cooler color now, run that where the highlights will go. You can do a little more throughout the whole thing if you're doing really light colors, like Aura here. I used an icy blue. If your character has a hotter temper or has truly flaming red hair, you'll want to go more sparingly on the cool color.
In some cases you can skip steps 8 and 9, but that's really going to depend greatly on your particular piece.
8: Go back to your base color and grab the brush, set it to size 3. If you're doing white, crystal, silver, or gray hair, you'll want to lighten the base color now so that it'll be far closer to the end result you desire. Blend everything over lightly.
9: If you're doing white, crystal, etc. lighten it again. Blend over in the places where you'll have more highlight.
10: Go back to the pen. Pick a highlight color, if you're doing white, crystal, etc. pick a good light color that'll brighten it up for the end result. If you're working with darker colors, pick one that'll be very subtle. Run it where the light will fall, especially where your highlights will be.
11: This is the one place with the hair where you can honestly get off with using some pure white. Strike it over the highlights to give it some extra shine.
Aura, guardian of The World from the .hack// series. And Just for the heck of it, I've added a bit of the Epitaph of Twilight in the background. I've also finished the fringe on her shawl at this stage.
Why did I pick Aura? When I decided to do a tutorial on painting fantasy hair in OC, Aura just came to mind. I may do a natural hair color tutorial at a later date, but truthfully the techniques are the same. The only thing that changes are the colors.