User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-4212769-20120331162339

I have another theory about the 3 Rathian/Rathalos:

It has to do with fertility. When they search for a mate their scales turn to pink/azure because of the extra-produced hormones till they have made babies and turn back to normal. They feed them as normal colored and the offsprings are green/red, too till they get old enough to be fertile. When they are too old to reproduce their scales turn to gold/silver what happens because of the lack of hormones produced in the sex organs.

About the Black Rathian:

I think it is a Subspecies. It is stronger and would extinct the normal Rathian. But they grow slower adult and fertile so they have to live longer before they can reproduce. That's why they are so few. They needed the time to grow stronger before they get fertile

What do you think?