Hey! You’re the first to ask for art help and it actually makes me quite flattered. ;A; I only started developing this style for coloring hair (and basically everything else) recently and slowly got to it through observation, so if I don’t make much sense please bear with me…
It’s basically very similar to other tutorials that can be easily found on DA. This utilizes Paint Tool SAI and assumes that you’re somewhat familiar with the program. Hope it helps…?
1) Fill in the base color and lightly shade with a darker color using an airbrush.
2) Use a regular brush and line out where the shadows should be. Pay attention to the light source.
3) Turn on the fringe effect. Then, using oil water + transparent color (the small box beside primary/secondary selected colors), start spreading the shadows from step 2. Give it volume I guess?
4) Lock the shadow layer and airbrush darker parts with an even darker color.
5) Time for finishing touches! Color the lineart to make it look more natural and not too bold (like my untouched harp right there haha). Add some subtle highlights with the pen tool, then take the skin color and lightly airbrush it onto the bangs to show reflection of color I guess. The final (optional) step is to adjust hue and saturation (go under Filters) if the colors aren’t very accurate.
I’m definitely no professional, but this is how I go by with most of my coloring ._.