Tate Modern has a new gallery devoted entirely to the work of Mark Rothko, and if there is a single element running through the room’s contents, it is raw, blistering anger. “The set of colossal canvases housed in Tate Modern’s Rothko Room originated, as every art-aware schoolboy knows, in a commission for the Four Seasons restaurant in the Seagram Building on New York’s Park Avenue,” and the story behind the commission explains what exactly it was that made Rothko so angry.