LordVishnu, concerning armament Haki in One Piece, Oda actually told us it is invisible and that we can see it because we are the readers and he wants us to know when a character uses it. How Releigh used it in sabaody is actually how everyone sees it being used, they don't. That is also why Don Flamingo found gear 4 so funny, because he just saw a bouncy inflated luffy that had steam coming off of him.
That's one of the ways you can get to it.
I see that your account is new. Don't forget to hit the 'Reader Mode' button once you're in the thread.