Blue is the most widely beloved color — but in nature, it’s the rarest hue of all. True, physics paints the sea and sky blue, but we can’t bottle this trick of the light. And blue pigment requires such complex chemistry that blue creatures, plants, and minerals are few indeed. Artists and kings have treasured blue dye like precious gold since the time of the pharoahs — and who today can help but marvel at a morpho butterfly in the rain forest or a blue jay at the window? Science journalist Kai Kupferschmidt has been enraptured by blue since childhood. In his quest to understand the mysteries of his favorite color, he takes readers on a vivid journey — from a biotech lab in Japan and a volcanic lake in Oregon to his native Germany, home of the last blue-feathered Spix’s macaws. Deep underground where blue crystals grow, and miles overhead where astronauts gaze at our “blue marble” planet — wherever he finds this alluring color, it always has a story to tell.