Board Thread:Naruto Discussions/@comment-3232093-20140617193601/@comment-4271790-20140818193417

Well Hagoromo's chakra is special (he is a Sage -- though that's just a name -- but can still use senjutsu chakra). After all, he was able to use a TSB before becoming the jinchuuriki of the TT. Wouldn't surprise me at all if Hagoromo was born with the Sharingan and eventually got the Rinnegan with his "special chakra." The way I see it Hagoromo may have inherited a different variant of Kaguya's one-eyed, nine-tomoe, Sharingan-powered Rinnegan (and by different, I mean a dual Sharingan and Rinnegan) and Hamura inherited her Byakugan.