Black or brown always dominated over red and blond but if you mixed red and blond it seemed random. Then I made some tests in CAS generating babies from various parents and it looked like it worked. I made black and brown 1 (dominant) and red and blond 2 ( recessive). I also changed the genetic value of my correctely binned custom hair and that seems to work as well. Renatus is correct, I've changed all my eyes in that way as well, to make them behave genetically correctly.
