Whale Shark

Photograph by Brian Skerry

The sweeping color of sea and sky, blue is a common thread in nature, seen in the cerulean of a whale shark (pictured here), the indigo of a stormy night, and the cobalt of a peacock's feathers. Over the centuries, the hue has come to represent calm, cold, mysticism, and sadness.

(For more pictures of the amazing colors of our world, buy the National Geographic book Life in Color.)