On a recent sparkling morning at Inkwell Beach, summer resident and retired Boston judge Ed Redd emerged from his daily swim and carefully considered a question: Does Martha’s Vineyard still retain a certain magic for African Americans — longtime residents and new visitors alike? Judge Redd, a barrel-chested, affable ambassador for the Polar Bears, the historic group that finds invigoration and spirituality in morning swims at the Inkwell from July 4 to Labor Day, didn’t pause for long.