I'm sure this has been done before, but whoever did it didn't release it as a material preset for everyone, so I started experimenting, I already knew I could create patterns using simple nodes and even images, but I wanted to try and make the color differences look more like natural streaks instead of the kind you get done at the salon...

So I used an fbm node and put the x and z scale at 0.004 and the y scale at 6.000 and the Octaves at 2.000... then I took the usual noise node and used a blender node to blend the noise with the fbm node... then I connected that to a ColorRamp node and gave the top two dark brown and the bottom two light brown then connected those to the color imputs on the hair node (not the specular though, there is nothing plugged into that). It is very simple but it turned out extremely good in my opinion. I also put more specular than with Aurora and Jessi_Short_Blonde... (Hair is Annelle Hair by Adorana; Character is Lyon by Danae), Hope you like it: