when I rendered the gorilla I use 127 half gray for the specular channels as I like it more natural silky
First I was talking about the base surface settings ( ds tab ) they are great when use with spot light but when use with uber environment they are much to strong, actually I never use white color for specular as it can pretty burn the colors while rendering
The colour in the specular options is just a blend colour, the blend slider below will blend from the colour set (at setting 0) and the colour settings set in garibaldi (at settings 1).
The hair shader is not very intuitive. I need to do some documentation/tutorial about what it all means.
Basically the Primary specular is extra shinny bit on the hair. Normally nearly white and small.
The secondary is the more wide specular that is more coloured and less bright.
There also a transmission reflection, which is off by default, this is basically for back lighting the hair.
Also the more traditional diffuse and ambient settings. Diffuse is good for a bit of fill, to simulate a multiscattered look.
For the specular settings:
Intensity is the overall brightness of highlight. Possible to set over 1 for extreme brightness.
Color and Color Blend are discribed above.
Shift is to move the highlight up and down the hair strand.
Width is how wide the highlight is.
There is also seperate opacity settings in the general tab. One for the beauty render and one for shadow map renders.
The localised shading rate in general is set high (low quality) as the nature of geometry means loose interpolated shading samples will be fine.
There also ambient occlusions settings which are good for short hair (assuming your not using the various urber occlusion things), There also a localised shading rate for occlusion here. Occlusion will slow down renders, especially for lots of hair strands
Here is a diagram (cross section of hair strand and light/reflection directions) of the general shading model.
Click thumbnail to see full-size image