It’s not often that an art museum can address a major gap in its collection with one bold move. So when the Fine Arts Museums of San Francisco made a deal early this year to acquire 62 works by 22 contemporary African American artists, the museums decided to produce a full-scale exhibition with catalog in four months—a fraction of the normal lead time—to celebrate. The result, “Revelations: Art from the African American South,” opened last week at the de Young Museum; it will be on view through April 1.