Why aren’t mammals as colorful as reptiles, birds, and fish?

Lizards, birds, and fish often have bright colors ranging from neon pink to deep purple, while most mammals are quite dull. So why don’t mammals match the bright colors of other animals?

Many factors ultimately lead to the browns, blacks, and whites that make up the fur of most mammals. The first is color expression. Matthew Shawky, an evolutionary biologist at Ghent University in Belgium, explained that animals generally express color in two main ways: pigmentally and structurally. Pigments are present in the skin and coat of the animal itself and reflect or absorb light to create specific colors. Structural coloration, on the other hand, involves nanoscale shapes and patterns on the surface of skin, feathers, and scales that can distort light and produce bright iridescent colors.

Animals use one method, or sometimes both methods, to represent color. But Shorkey says mammals don’t actually use either. Of the many pigments that produce color, including carotenoids, porphyrins, and pterins, mammals have only one type: melanin. The presence of that one pigment produces all the colors seen in mammals, Shawkey said, and its absence produces the white areas seen in animals such as zebras and pandas.

you may like

Furthermore, the composition of the hairs that make up mammalian fur limits the structural colors that mammals can display. Hair is not a complex structure like feathers, scales or skin, so it’s not surprising that it can’t generate the nanoscale patterns needed for structural color, Shorkey noted.

For example, the mandrill (Mandrillus sphinx) breaks the monotonous mammal rule with bright reds and blues, having such colors only on the areas without fur. Sloths may have green spots, but the color comes from the algae that grows on their fur, rather than from the pigment or structure of the fur itself.

evolution of color

So why don’t most mammals have the tools to produce bright colors? One hypothesis is that when mammals first evolved, dinosaurs were the apex predators and mammals were the prey. To avoid being eaten, mammals have been (and most still are) primarily nocturnal animals for more than 100 million years.

Those millions of years have had a huge impact on the appearance of mammals. In a 2025 study co-authored by Shawkey and published in the journal Science, the team compared pigment-storing structures called melanosomes in modern mammals to preserved melanosomes found in six Jurassic and Cretaceous mammal fossils. They discovered that all mammalian fossils were shades of brown or gray.

These prehistoric animals lived primarily in the dark, so dark colors likely helped the mammals avoid predators. “Any bright color would not have been chosen,” Shawkey told Live Science.

In the 66 million years since the Nonavian dinosaurs went extinct, mammalian diversity has exploded to more than 6,000 species. Currently, there are mammals, both nocturnal and diurnal, that have no natural enemies. However, most mammals remain brown, gray, or black.

Ted Stankowicz, a behavioral and evolutionary ecologist at California State University, Long Beach, said this may be because most mammals lack color vision. Researchers speculate that during the age of dinosaurs, mammals may have sacrificed some of their color vision for better night vision. Most mammals still have dichromatic vision. This means the eye only has two of the three types of cones that help it perceive color. Dichromats cannot see colors such as red, orange, turquoise, and purple, and generally cannot see colors as highly saturated as trichromats, who have all three types of cones.

What to read next

Animals primarily use color for purposes such as attracting mates, intraspecific communication, blending into camouflage, and telling predators that they are poisonous or dangerous, but this does not work if their partners or predators cannot see the colors they are using. Some mammals have actually used this lack of color vision to their advantage. For example, tigers appear orange to our trichromatic eyes, but appear green to mammalian prey, so they are perfectly camouflaged in grass when hunting.

Instead of using bright colors, many mammals use patterns and contrasting colors, such as black and white or brown and yellow, to signal each other, Stankowicz said. For example, skunks and polecats use black and white spots or stripes to let predators know they have a scent trick up their sleeve. Known for its unique markings, this African wild dog has a distinctive white tail, which researchers believe is used to signal when hunting. Known for its high-contrast black, reddish-brown, and orange-yellow markings, the Indian giant squirrel may use this as camouflage against various types of predators.

Mammals may have less reason to regain color vision because they have adopted new methods of color signaling. (The few mammals with trichromatic vision, such as humans and primates, including some monkeys, have evolved color vision for very specific reasons.) Stankowicz pointed out that the few mammals that display bright blues and reds, such as baboons, golden macaques, and mandrills, also have some of the best color vision.

Fluorescence and rainbow colors

Recent research has revealed some other exceptions. For example, many mammals fluoresce under ultraviolet light, which is undetectable to the human eye, while some others can. Additionally, evolutionary biologist Jessica Dobson of Ghent University and her colleagues have discovered iridescence in a small number of mammalian species not previously known to have this shimmering feature.

“It was a lightbulb moment,” Dobson said of the iridescent discovery, which occurred when she opened a drawer in the museum and sunlight hit the preserved fur of several species of tropical rats at just the right angle. Although Dobson isn’t sure whether these iridescent colors serve evolutionary purposes, she said it’s interesting to know there are still mysteries of mammalian color to unravel.

“Once you start looking, you find that mammals are more colorful than we think,” Dobson says.

Animal Quiz: Test yourself with these fun animal trivia questions