Hair color is an important element. It defines a character quite well most of the time. Below are various types of hair color displayed how you would present them in a manga. Colors range from white to jet black hair.
1) White Hair – Just the outline of the person’s hair
2) Blonde Hair – Add lines to the hair where you would put highlights
3) Tone Hair – Hair with tones be it physically added or digitally inserted. Check out Tones: Basics for more details.
4) Black Hair with Highlights – White areas around the top of the head and some near the bottom if coloring longer hair.
5) Black Hair with White Hair Lines – Hair lines that would normally be black on lighter hair is now white on black hair. Just think of it as an outline of the hair. This can be a bit tricky depending on what you’re doing.
If you had a regular white haired person, to get this effect, just invert the image – then recolor the face and other parts with black.
I would suggest you color black lines around your penciling of your hair lines. It’ll save you a lot of trouble later. :)