When author Phyllis La Farge and photographer Magdalena Caris recently took a journey from the city of Xalapa in the state of Veracruz to the town of Coatepec, they noted that on the facades of countless public and private buildings, improvised murals had been painted. The wit and exuberance of these wall paintings, whether commercial or simply decorative, suggested an urban visual lingo that could be traced to the ancestral murals of pre-Columbian Mexico, and La Farge and Caris decided that they deserved closer study. Somewhere between a scholarly investigation and a travel book, Painted...