Peter Max, whose colorful, psychedelic pop art expressed the optimism of the “flower power” movement of the 1960s and graced everything from postage stamps to a cruise ship, has died at 88.Max died on Monday, his son, Adam Max, said in a written statement on Wednesday. No cause was given.“We will remember his extraordinary creativity, his warmth, his curiosity, and the way he saw beauty and possibility everywhere,” Adam Max wrote in the statement. “His art became part of American culture, but the man behind that art – the father we knew and loved – is the person we will...