Hallelujah, and better late than never, are among the responses one may have to "Revelations: Art from the African American South," a truly outstanding, long overdue exhibition at the de Young Museum. The occasion for the show is FAMSF's recent acquisition of 62 sculptures, paintings, drawings, ingenious, emotionally charged assemblages, quilts from Gee's Bend, and prints based on them, by 22 Southern-born, late-19th and 20th century, African American artists.