Stop in for a cup of coffee

Dont want to come off like a know-nothing-er, but the o-rings are some kind of nitrile or something, correct? The ac from the 97 had all black o-rings buna-n i think they call them.
Yeah, this truck had the black buna-n rings, but I replaced them all with the green nitrile one, since they seal better. Whenever I do a system, I change all o ring seals...