Countershading

Countershading is a coloration pattern in which an animal’s upper surface is darker than its underside. It can reduce the appearance of shape by compensating for light falling from above.

Self-shadow concealment: Camouflage produced when coloration reduces the visual cues created by an object's own shading. Countershading can offset the dark underside that overhead light would otherwise create.
Natural selection: A change in the frequency of heritable traits when individuals differ in survival or reproductive success. Predation and other visual pressures can favor countershading over generations.
Great white shark: A large predatory shark with a gray upper body and pale underside. Its contrasting back and belly are a familiar marine example of countershading.
Reverse countershading: A coloration pattern in which an animal’s underside is darker than its upper surface. It reverses the usual light-to-dark arrangement and may suit unusual lighting conditions.
Animal camouflage: Adaptations that reduce an animal’s chance of being detected or recognized by predators, prey, or other observers. Countershading is one form of concealment within the broader range of animal camouflage.
Predator–prey interaction: An ecological relationship in which one organism hunts and consumes another. The concealment value of countershading depends partly on the vision and behavior of predators and prey.
Penguin: A flightless seabird adapted for swimming, often with a dark back and pale underside. Its coloration provides a clear countershaded pattern in an aquatic setting.
Aposematism: A conspicuous signal that warns predators of an organism’s toxicity, danger, or unprofitability. Countershading generally reduces visibility, whereas aposematic coloration advertises a warning.
Dorsal–ventral gradient: A gradual difference in color or brightness between an organism’s back and underside. This pigment gradient is the typical physical arrangement that produces countershading.
Developmental plasticity: The capacity of an organism to develop different traits in response to environmental conditions. Environmental light can influence pigmentation patterns in some animals, alongside inherited differences.

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