User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-5020152-20120829202114/@comment-4212769-20120829213749

You know my theory, right?

My theory includes that because Azure/Pink is in that case more or less a mating season form. When mating season commences EVERY Rathalos and Rathian changes. That means we will only see Azure and Pink ones. Because they are mating for life both grow old and lose their fertility so that both turn to Silver and Gold.

An update about why there is no temporare pair of Gold and Red/Green and Silver is maybe that they search partners that are about the same age.

BTW, your theory is invalid right from the start because only because they are different subspecies it doesn't mean they cannot pair up and reproduce. When even Tigers and Lions can reproduce with each other then those can, too. But in opposite to Ligers bastards of those can still reproduce because both are still the same species. So we would see some mixtures of those subspecies, too.