User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-5020152-20120829202114/@comment-4212769-20120829224851

Because it's a poster.

I don't know if you know my theory (if not search it at page 10 or so) but that Common Rathalos could be a non-fertile means an adolescent Rathalos. As the mating season form's color change is mainly caused by hormones the hormone gland of those adolescent Rathalos aren't as active as a fertile one means it doesn't get the color change.