The idea of a “hard-edged” watercolor seems dangerously close to an oxymoron, but such are the works for which the American painter Al Held became known. His large paintings feature dynamic swaths of bright yellows and blues. Architectural lines slip seamlessly over one another thanks to Held’s medium of choice. The title of one of the works in this show at White Cube, Particular Paradox, describes Held’s art to a T. —Clara Molot