You're absolutely right. Getting the hair data right (groom, strand color, little fiber variations) is just as difficult as implementing the right shading model

You're absolutely right. Getting the hair data right (groom, strand color, little fiber variations) is just as difficult as implementing the right shading model. My renders are currently a bit lacking in that regard - I'm not an artist, but I'll try to look out for that in the future. Adding some subtle random variation between fibers is definitely doable. As far as the hair color goes, I was following measured absorption coefficients of real human hair. Eugene d'Eon's paper "An Energy-Conserving Hair Reflectance Model" contains measured absorption coefficients for the pigments Eumelanin and Pheomelanin, which are responsible for human hair color. By mixing their concentrations, you can reproduce any hair color found in real life. It's difficult to find the mixtures that are just right though, and it's likely that I was a bit off for the blonde hair render :) I'll tweak it some more in the future.