Why do penguins have black backs and white bellies?

Penguins’ black-and-white plumage is a classic example of countershading. In the ocean, a dark back is harder to see from above against the depths, while a pale belly is harder to see from below against sunlight near the surface. This makes them less visible to predators and to prey such as fish and krill. The pattern is found in many swimming animals, including sharks and whales, because it works well in open water. In penguins, the coloration is especially useful because they spend much of their lives swimming and diving rather than flying.