Two of the stars of Lincoln Center Theater’s Broadway revival of “South Pacific” wore their politics on their sleeves at the show’s opening night party on Thursday.Kelli O’Hara, toplining as the navy ensign who just can’t wash that man right out of her hair, made her presidential choice clear as she talked up the modern day resonance of “Pacific,” the 1949 Rodgers and Hammerstein tuner about Americans in wartime struggling to overcome innate racism. “I think it’s no accident how relevant it is. Here we are at war, and we’re about to elect a black president,” she predicted. Matthew Morrison, meanwhile, wore an Obama button on his lapel. “We’re trying to get him to come to the show!” he said.