Animal color has several physical causes. Pigments are one of them, and they are not the whole story. Some colors come from pigments that absorb certain wavelengths of light, some come from microscopic structures that interact with light, and many bright animals use both. There is no single pigment that explains colorful animals as a group, and the reasons an animal is colorful, such as camouflage, courtship or warning, depend on the species and its surroundings.
Three ways animals produce color
Most explanations of animal color fall into one of three categories. The table below compares them before the details.
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| Mechanism | How it produces color | Examples given by the sources | What can change it |
|---|---|---|---|
| Pigmentary color | A pigment absorbs some wavelengths and reflects others; the reflected light is what an observer sees | Melanin (dark and brown tones); carotenoids (yellow, orange, red, pink); pterins (often bright coloration) | Pigments can break down and alter color; carotenoids often come from food |
| Structural color | Microscopic structures in feathers, scales, shells or skin scatter or reflect particular wavelengths | Blue morpho butterfly wing scales, which have tiny grooves | Color persists while the structure is intact; damage to the structure can still change appearance |
| Combined color | A structure and a pigment work together to produce one hue | Many green bird feathers: blue structural color over yellow carotenoid pigment | Changes to either component can shift the overall color |
Pigments: melanin, carotenoids and pterins
Melanin is the pigment most often linked to dark and brown tones. Carotenoids produce yellow, orange, red and pink, and many animals obtain them from what they eat rather than making them. Pterins are a separate group, usually made by the animal itself, and they are often associated with bright coloration. Pigment color is a matter of which wavelengths are absorbed, so a pigment’s hue is set by its chemistry.
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Structural color: why some blues have no blue pigment
Structural color comes from physical arrangement rather than chemistry. The Smithsonian attributes the blue of the blue morpho butterfly to tiny grooves in its wing scales, which interact with light to reflect blue. Many blue feathers and scales in animals work this way, which is why a blue patch does not necessarily contain a blue pigment.
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Combined color: the green bird feather
The American Museum of Natural History describes many green bird feathers as combining blue structural color with yellow carotenoid pigment. Neither component is green on its own; the eye sees green because the two are layered. This is why describing a bright color as purely pigmentary or purely structural is often inaccurate.
Iridescence and why some colors shift
Iridescence is a form of structural color. The apparent hue changes with viewing angle because light reflected from the structure interferes differently at different angles. A surface that looks blue from one position can look green or violet from another, and a pigment alone does not produce that shift.
Durability differs between the two mechanisms. The Smithsonian notes that structural colors do not fade while the relevant physical structure is preserved, whereas pigments may break down over time. A structure that is physically damaged can still lose its appearance, so structural color is durable only as long as the structure is intact.
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What coloration does for animals
Color can make an animal harder to see against its background, help it attract a mate, or warn or deter a predator. The same color can serve different functions in different species, so a bright appearance should not be labeled a signal without evidence for that species.
Pterin coloration shows why. A peer-reviewed review of pterins describes warning and reproductive functions, camouflage in some species, and a case where a red eye pigment serves vision rather than display. Fish coloration can also contribute to camouflage and to social and reproductive interactions, and fish color depends on genetics, pigments, structure and diet.
A broad pattern across land vertebrates
The National Science Foundation summarizes research by Zachary Emberts and John Wiens that looked at land vertebrates. The study reports an association between sexual coloration and ancestors that were active during the day, and between warning coloration and ancestors with nocturnal lifestyles. The NSF places the study’s scope at about 40,000 land-vertebrate species over more than 350 million years of evolution. That figure describes the group studied, not the number of colorful species.
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John Wiens, the study’s senior author, put the point this way:
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsIndependent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.“It doesn’t matter how a species produces the colors. The way that a bird makes red is different from how a lizard makes red, but this general pattern of day-night activity still works.”
Examples that show the mechanisms at work
- Flamingos: Carotenoids from food contribute to the pink of adult feathers. Chicks begin gray, so diet-driven color appears over the animal’s life.
- Blue morpho butterfly: The blue comes from microscopic grooves in its wing scales, not from a blue pigment.
- Green bird feathers: Blue structural color over yellow pigment produces green.
- Fish: Chromatophores hold or reflect color, and nervous or hormonal control can move pigment granules within them, changing appearance.
- Cuttlefish and other cephalopods: Chromatophores can change size or pigment distribution quickly, producing shifting shades and patterns.
Colors humans cannot see
Human vision does not capture every color animals display. The Natural History Museum of Utah notes that many birds can perceive ultraviolet wavelengths that people cannot see without equipment. A patch that looks plain to a person may be bright to a bird, so a human’s view of an animal’s color is incomplete.
Where the evidence stops
- No single pigment explains colorful animals as a whole.
- No widely cited statistic measures how many animals are colorful. The 40,000-species figure refers to the land vertebrates in the Emberts and Wiens study.
- The land-vertebrate pattern is a broad evolutionary association, not a rule that applies to every colorful species.
- Species-specific explanations should be checked against research on that species before being extended beyond the examples above.
For readers who want to go further, the Smithsonian, the American Museum of Natural History, the National Science Foundation and the Natural History Museum of Utah each publish general explanations of animal color that are suitable starting points.
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