Kerry James Marshall's Mementos is a sadly beautiful reminder of the Civil Rights movement - a reminder that provokes us to question the closed-book, "memorial" status that history has attributed to this moment of inspired social action. In Marshall's banner-like paintings appear bittersweet visions of 30 years past, in which the heroes of modern black history appear as ghosts frozen in time, and in oversized stamps, the empowering slogans of the...