The iconic art of Peter Max defined the psychedelic experience of the 1960s, or at least the broad commercial expression and perception of it: Colorful imagery of gurus, sages, runners, flyers, Zen boats, snowcapped mountains, planets, stars and sunbeams, Max’s cosmic posters adorned the walls of college dorm rooms and major museums alike. Opening on April 7, the Museum at Bethel Woods presents “Peter Max: Early Paintings,” bringing together for the first time the major collections of Robert Casterline and Shelly Fireman.