These are not bright times. We see the world in shades of gray. So gallerygoers may be especially interested in artists who work in mixtures of black and white—in what for centuries has been known as grisaille. Of course, I’m not so sure that gray times inspire a taste for gray paintings. Formal values are not necessarily so closely related to social experience. And yet the thought has crossed my mind as I contemplate “Grisaille,” a group show currently at Luxembourg and Dayan in New York.