>>3288257My advice for highlighting is make ample use of curve and blur tools. I usually outline the highlight in curves, fill the outline with a lighter shade of the hair's base color, then draw two curved bands of an even lighter shade + a pastel color (I like yellow for Nino) to give the highlight a slight gradient glare. At that point, your hair has four colors not including linework outlines: the base color, highlight shade 1, highlight shade 2, and highlight glare.
From there, I merge all of the highlight layers together and blur the colors until it looks good, then I merge the completed highlight onto the base hair and blur the edges into the base hair color. Touch-ups may be required at any stage, and you may wish to use translucent/overlay layers.
I used this method for pic related. It's not perfect, but it's better than my original method of haphazardly using an airbrush with increasingly light shades of pink.
