What is it about the color blue? Blue is our favorite color globally—the darling of artists since the time of the pharaohs. So it’s startling to turn to the realms of nature and discover that “true” blue is truly rare. The sea and sky are blue, but we can’t bottle this trick of physics. And the few creatures, plants, and minerals that appear blue are almost all deceiving us. There’s no blue pigment in a blue jay—it would be brown but for how its feathers distort light. Kai Kupferschmidt has been enraptured by blue since childhood. In Blue, he invites readers on his globe-trotting quest to understand his favorite color— from Kyoto, where scientists are trying to engineer a blue rose, to Brandenburg, where conservationists hope to save the “little blue macaw.” Deep underground where blue crystals grow and miles overhead where astronauts gaze at our “blue marble” planet-wherever he finds this alluring color, it has a story to tell.