Yeah, I do something similar -- although I haven't tried to go back and add in additional white highlights with white pencil or ink, as it looks like was done in that sample. I should try experimenting with that!
I based my technique for black or very dark brown hair on the way Wendy did it for the comics. That means doing the basic foundation of the black hair color in the inking phase, and leaving highlight-areas for coloring. I usually use the "formula" that "black hair" = black with blue highlights, while I tend to think of black hair with brown highlights as being "very dark brown".
That usually works for me in cases where the areas of highlight are pretty small, overall. I just use one color, and haven't experimented yet with putting white highlights in too. But when I've done a larger figure (like a bust portrait), I usually use two blues -- the first one lighter, and then the second darker, to suggest gradations of shading even within the highlight area.
I ended up doing this because of the effect I mentioned above, which is that because of the paper I use, the Copic black marker doesn't give me a "solid" black. Light bounces through it in the scanning process. Because I laser-print my inks to color them, that gives me a very solid black
