It can be very difficult to get right. If you use the ambient colour to turn a hair texture dark, you lose the highlight/sheen that's so essential to an authentic asian look. I've been trying for months to get the right look for an Indian character: the hair issues are similar. As far as I can tell, you'd have to create a custom texture. You'd need a higher contrast texture than looks right for caucasian characters...and that would create challenges in lighting, because if your lights don't match the hair highlights it'll look all wrong. The other option would be to work in the P5 hair room. That at least allows you to control the hair texture/highlight to a greater extent than texture-mapped models.