Why do penguins have black-and-white plumage?

Penguins spend much of their lives in the ocean, where camouflage matters more than on land. A dark back blends with the deeper water when seen from above, while a white belly blends with the bright surface light when seen from below. This countershading is common in many marine animals, but penguins are a classic example. Their black-and-white pattern is especially useful for species such as emperor penguins and Adélie penguins. The pattern is functional, not decorative, and it reflects the pressures of life in the sea.