since my shader is quite a complicated thing, I want to give you some additional hints about the usage...
The shader consists of four components:
where R means a direct (white) surface reflection (first highlight), TT the forward transimission (especially importantant if lit from back) and TRT a strong secondary highlight. These three modes are strongly realted to the model of Marschner et al.
The diffuse and ambient components are similar to the usual Kajiya&Kay model and ar NOT physically correct.
The total outgoing intensity is calculated as follows:
Out=Light*scale_total*(scale_R*R + scale_TT*TT + scale_TRT*TRT + scale_diffuse * diffuse + scale_ambient*ambient)
With the scale parameters each component can be scaled individually. Note, that for physically based hair both diffuse and ambient components should not contribute too much intensity.
The most important parameters for changing the hair color are the absorption coefficients. They give you the right colors for both the TRT and the TT components. The diffuse and ambient colors should be set according to this absorption (see the tutorial).
Beside the color one might want to have more (less) radiant hair. This can be done by changing the scale of the highlights (scale_R,TT,TRT) and their widths (width_R,TT,TRT; the bigger the numbers the smaller the width !!!).
For realistically looking hair/fur one needs furthermore variation of the shading parameters. To get more "texture" try to vary:
-index of refraction (slightly !!!)
-the diffuse/ambient colors