It never rains in Onyx. Instead, the sky changes color. Mondays and Thursdays it’s azure. Tuesdays it’s royal blue. Wednesdays and Saturdays: cyan. Sunday’s sky is nearly white, with a touch of battleship gray. Fridays the sky can be anything from cornflower to wheat. Whatever citizens wish, that’s the color of Friday’s sky. Sarah has been a citizen of Onyx since she was born five-and two-thirds...