Stella - there are a few ways to do it - but they are complicated.
Successive layers of colour-burn and colour dodge may work; or a highly contrasted layer as a blending layer that "screens" or "multiplies" selective areas. For the most part most of the good hair makers seem to use high resolution images of real hair to make their textures - or they are using a sophisticated "tube" or "brush" that I myself don't have installed.
Texture making is a very personalised thing. Each artist has their own look or style. Hair is no different. I think you will be best served by experimenting with images of real hair and finding what you like best.
see this tuto - it is for a different game - but works just as well for TS2