Padi's new citizen-science diving programme is turning holidaymakers into ocean researchers as warming seas put reefs, sharks and rays under mounting pressure. They say that the sea that surrounds Okinawa, Japan, has its own shade of blue, created by a heady mix of clear water and limestone seabeds. Yet from my perch at the top of Cape Manzamo, a lava-stone promontory on Okinawa's main island, I could count at least five stunning pantones. Beneath that prismatic surface, however, the reefs