[Toraspanda]

Greens are female, but infertile because they chew firestone. Mirrim was the first female Green Rider in the 9th Pass, but in previous passes women had also ridden Greens (see Deberaone of the major characters in Red Star Rising/Dragonseye, and her Green Monarth). For some reason women had stopped impressing Greens, and that was why Mirrim was the first woman in living memory to do so.
Golds are only ridden by women, and Bronzes, Browns and Blues are ridden by men. Blue Riders and male Green Riders are always, or nearly always homosexual or bi-sexual.