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Animal colors come from pigments, from microscopic structures that bend and scatter light, or from both working together. Pigments explain part of the story, but no single pigment accounts for animal color as a whole. The pigment most often blamed, melanin, mainly produces dark and brown tones. Bright reds, yellows and blues usually need other explanations.
How animals make color
Scientists generally sort animal coloration into three mechanisms. Many colorful animals use more than one at a time, so it helps to know what each one does before deciding which explains a particular animal.
1. Pigmentary color
A pigment absorbs some wavelengths of light and reflects others. The reflected wavelengths are what an observer sees as color. Three pigment groups come up repeatedly:
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- Melanin commonly produces dark and brown tones.
- Carotenoids contribute yellow, orange, red and pink. Most animals cannot make them and acquire them from food, so diet can change how colorful an animal looks.
- Pterins are commonly produced inside the animal and are often linked with bright coloration.
2. Structural color
Here the color comes from the shape of the surface rather than from a chemical that absorbs light. Microscopic structures in feathers, scales, shells or skin interact with light and reflect or scatter particular wavelengths. The Smithsonian attributes the blue of the blue morpho butterfly to tiny grooves in its wing scales. Nothing in those scales is blue in the way a paint is blue; the groove spacing is what selects the wavelengths that reach your eye.
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3. Combined color
Many animals layer both mechanisms. The American Museum of Natural History explains that many green bird feathers combine blue structural color with yellow carotenoid pigment. Blue structure reflects blue light, and yellow pigment filters out much of the blue-violet range, so the combined result looks green. Neither part alone would produce that green.
Iridescence and durability
Iridescence is a form of structural color. The hue appears to shift as the viewing angle changes, because light reflected from the structure interferes differently at different angles. This is the most useful visible clue that a color is structural rather than pigmentary.
The two mechanisms also age differently. The Smithsonian notes that pigments may break down and alter an animal’s color, while structural colors do not fade as long as the physical structure is preserved. The qualification matters: damage to the structure, such as worn or abraded scales, can still change the appearance.
| Feature | Pigmentary color | Structural color |
|---|---|---|
| Physical basis | A pigment absorbs some wavelengths and reflects others | Fine surface structures interact with light and reflect or scatter particular wavelengths |
| Typical colors named in the sources | Dark and brown (melanin); yellow, orange, red and pink (carotenoids) | Blue and iridescent colors, such as the blue morpho butterfly |
| Hue change with viewing angle | Not stated in the sources reviewed | Can shift with viewing angle (iridescence) |
| Effect of aging or damage | Pigments may break down and alter color | Does not fade while the structure is preserved; structural damage can still change appearance |
| Typical origin | Made by the animal (pterins, melanin) or obtained from food (carotenoids) | Built into the shape of feathers, scales, shells or skin |
What bright color is for
Color can serve several purposes, and the function depends on the species and context. Depending on the animal, it can make the animal harder to see against its background, attract a mate, or warn or deter a predator. Coloration in fish can also be involved in camouflage and in social or reproductive interactions.
A bright color is not automatically a signal. Pterin coloration shows why. A peer-reviewed review of pterin pigments describes warning and reproductive functions, camouflage in some species, and a case where a red eye pigment serves vision rather than display. The same chemical family can therefore do different jobs in different animals.
A broad pattern across land vertebrates
A U.S. National Science Foundation summary of a study by Zachary Emberts and John Wiens, published in 2022, covered about 40,000 land-vertebrate species spanning more than 350 million years. The NSF presents those figures as context for the group the study examined, not as a count of colorful species. The study reported an association between sexual coloration and ancestors active during the day, and between warning coloration and ancestors with nocturnal lifestyles.
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This is a broad evolutionary pattern for that group. It is not a rule that applies to every colorful species. Wiens, the study’s senior author, put the point this way: “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 worth knowing
- Flamingos: Carotenoids from food give adult feathers their pink color. Chicks begin gray, so diet shapes how the adult color appears.
- Blue morpho butterfly: Microscopic grooves in its wing scales produce the blue, with no blue pigment required to explain it.
- Green bird feathers: Blue structural color combined with yellow pigment produces green.
- Fish: Color depends on genetics, pigments, structure and diet. Chromatophores hold or reflect color, and nervous or hormonal control can move pigment granules within them, changing the animal’s appearance.
- Cuttlefish and other cephalopods: Chromatophores can rapidly change size or pigment distribution, producing shifting shades and patterns.
Human eyes miss part of the picture
The Natural History Museum of Utah notes that many birds can perceive ultraviolet wavelengths that humans cannot see unaided. A bird that looks plain to you may be displaying a pattern clearly visible to another bird. When you judge whether an animal is colorful, you are judging it through human vision only.
Checking a claim about a specific animal
The general mechanisms above explain how color is produced, but they do not tell you why a particular species looks the way it does. For a specific animal, check three things:
- Whether the color is pigmentary, structural or both, using the viewing-angle and fading clues above.
- Whether the animal can acquire the pigment from food, since diet may change its color.
- Whether the proposed function (camouflage, courtship or warning) is supported by studies of that species or group, not just by its appearance.
Examples in popular articles, including the ones here, should be checked against species-level research before being extended to other animals.
The Bottom Line
Animal color is not one pigment’s work. Pigments such as melanin, carotenoids and pterins produce many colors, structural features produce others such as the blue of the morpho butterfly, and many animals combine the two. The function of a bright color has to be tested species by species.
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