Camouflage is a method of cryptic or concealing coloration that allows an otherwise visible organism or object to remain indiscernible from the surrounding environment through deception. Examples include a tiger's stripes and the battledress of a modern soldier. The theory of camouflage covers various strategies which are used.
Cryptic coloration is the most common form of camouflage, found to some extent in the majority of species. The simplest way is for an animal to be of a color similar to its surroundings. Examples include the "earth tones" of deer, squirrels, or moles (to match trees or dirt), or the combination of blue skin and white underbelly of sharks via countershading (which makes them difficult to detect from both above and below). More complex patterns can be seen in animals such as flounder, moths, and frogs, among many others.
The type of camouflage a species will develop depends on several factors:
Animals produce colors in two ways:
Cryptic coloration can change as well. This can be due to just a changing of the seasons, or it can be in response to more rapid environmental changes. For example, the Arctic fox has a white coat in winter, and a brown coat in summer. Mammals and birds require a new fur coat and new set of feathers respectively, but some animals, such as cuttlefish, have deeper-level pigment cells, called chromatophores, that they can control. Other animals such as certain fish species or the nudibranch can actually change their skin coloration by changing their diet. However, the most well-known creature that changes color, the chameleon, usually does not do so for camouflage purposes, but instead to express its mood.
Beyond colors, skin patterns are often helpful in cryptic coloration as well. The Craik-O'Brien-Cornsweet illusion describes visual perception as occurring through contrasts of outlines. One recognizes a dog, for example, not by its color as much as by its shape. Often what matters most for good cryptic coloration is to break up the outline of a creature's body. This can be seen in common domestic pets such as tabby cats, but striping overall in other animals such as tigers and zebras help them blend into their environment, the jungle and the grasslands respectively. The latter two provide an interesting example, as one's initial impression might be that their coloration does not match their surroundings at all, but tigers' prey are usually color blind to a certain extent such that they cannot tell the difference between orange and green, and zebras' main predators, lions, are color blind. In the case of zebras, the stripes also blend together so that a herd of zebras looks like one large mass, making it difficult for a lion to pick out any individual zebra. This same concept is used by many striped fish species as well. Among birds, the white "chinstraps" of Canada geese make a flock in tall grass appear more like sticks and less like birds' heads.
In nature, there is a strong evolutionary pressure for animals to blend into their environment or conceal their shape; for prey animals to avoid predators and for predators to be able to sneak up on prey. Natural camouflage is one method that animals use to meet these. There are a number of methods of doing so. One is for the animal to blend in with its surroundings, while another is for the animal to disguise itself as something uninteresting or something dangerous.
There is a permanent co-evolution of the sensory abilities of animals for whom it is beneficial to be able to detect the camouflaged animal, and the cryptic characteristics of the concealing species. Different aspects of crypsis and sensory abilities may be more or less pronounced in given predator-prey pairs of species.
Some cryptic animals also simulate natural movement, e.g., of a leaf in the wind. This is called procryptic behaviour or habit. Other animals attach or attract natural materials to their body for concealment.
A few animals have chromatic response, changing color in changing environments, either seasonally (ermine, snowshoe hare) or far more rapidly with chromatophores in their integument (the cephalopod family).
Some animals, notably in aquatic environments, also take steps to camouflage the odours they create that may attract predators.
Some herd animals adopt a similar pattern to make it difficult to distinguish a single animal. Examples include stripes on zebras and the reflective scales on fish.
Camouflage was not in wide use in early western civilization based warfare. 19th century armies tended to use bright colors and bold, impressive designs. These were intended to daunt the enemy, attract recruits, foster unit cohesion, or allow easier identification of units in the fog of war. Another very important reason for the brightly colored uniforms was that before the invention of smokeless powder, it was very hard to decide which unit someone belonged to by looking at their uniforms; furthermore, even in the best of circumstances, the colors tended to be covered by soot after the shooting had gone on for a while. All the dust that the marching units stirred up had a similar effect.
Smaller, irregular units of scouts in the 18th century were the first to adopt colors in drab shades of brown and green. Major armies retained their color until convinced otherwise. The British in India in 1857 were forced by casualties to dye their red tunics to neutral tones, initially a muddy tan called khaki (from the Urdu word for 'dusty' as the tan matched the local dust). White tropical uniforms were dyed by the simple expedient of soaking them in tea. This was only a temporary measure. It became standard in Indian service in the 1880s, but it was not until the Second Boer War that, in 1902, the uniforms of the entire British army were standardized on this dun tone for battledress. Other armies, such as the United States, Russia, Italy, and Germany followed suit either with khaki, or with other colors more suitable for their environments.
Camouflage netting, natural materials, disruptive color patterns, and paint with special infrared, thermal, and radar qualities have also been used on military vehicles, ships, aircraft, installations and buildings. A striking example of this is the dazzle camouflage used on ships during WW I.
Ghillie suits are worn by military special forces units to take camouflage to the next level, combining not just colours, but twigs, leaves and other foliage.