A globe-trotting quest to find blue in the natural world - and to understand our collective obsession with this bewitching colour. Blue is a rare colour - natural blue, that is. From morpho butterflies in the rain forest to the blue jay flitting past your window, vanishingly few living things are blue - and most that appear so are doing sleight of hand with physics or complex chemistry. Flowers modify the red pigment anthocyanin to achieve their blue hue. Even the blue sky above us is a trick of the light. Yet this hard-to-spot accent colour in our surroundings looms large in our affections. Science journalist Kai Kupferschmidt has been fascinated by blue since childhood. His quest to find and understand his favorite colour and its hallowed place in our culture takes him to a gene-splicing laboratory in Japan, a volcanic lake in Oregon, and to Brandenburg, Germany - home of the last Spix's macaws. From deep underground where blue minerals grow into crystals to miles away in space where satellites gaze down at our "blue marble" planet, wherever we do find blue, it always has a story to tell.