Lizards, birds and fish often have vibrant colors, from neon pink to deep violet, but most mammals are rather dull. So why don’t mammals match the vibrant colors of other animals?
A number of factors culminate in the browns, blacks and whites that make up most mammal coats. The first has to do with color expression. Matthew Shawkeyan evolutionary biologist at Ghent University in Belgium, explained that animals generally express color in two main ways: through pigments and through structures. Pigments are found in the skin and fur of the animal itself and reflect and absorb light to create specific colors. Structural coloration, on the other hand, involves nanoscale shapes and patterns on top of skin, feathers, or scales that can distort light to produce bright, iridescent colors.
Animals can use one method, or sometimes both, to express color. However, according to Shawkey, mammals don’t really use either. Of the many color-producing pigments – such as carotenoids, porphyrins and pterins – mammals have only one type: melanin. The presence of the one pigment generates all the colors seen in mammals, Shawkey said, and its absence creates the white areas seen in animals such as zebras and pandas.
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Also, the composition of the hairs that make up mammals fur limits the structural colors that mammals can display. Hair is not a complex structure like feathers, scales and skin are, so it is not surprising that it cannot produce the nanoscale patterns necessary for structural coloration, Shawkey noted.
For example mandrills (Mandrillus sphinx), who break the sad mammal rule with theirs bright red and bluehave those colors only on spots without fur. Slothwhich sometimes have green spots, get this color from algae growing on their fur, not from pigments or structures on the hairs themselves.
Evolution of color
So why don’t most mammals have the tools to create vibrant hues? One hypothesis is that when mammals first evolved, dinosaurs were apex predators and mammals were prey. To avoid being eaten, mammals spent more than 100 million years as primarily nocturnal animals (and most remain so today).
These millions of years had a major impact on the appearance of mammals. In a 2025 study co-authored by Shawkey and published in the journal Sciencea research team compared pigment-storing structures called melanosomes in modern mammals with preserved melanosomes found in six Jurassic and chalk-age mammal fossils. They found that all the mammal fossils were a shade of brown or gray.
Because these prehistoric animals lived mainly in the dark, darker colors would have helped mammals avoid predators. “Any bright color would have been selected against,” Shawkey told LiveScience.
In the 66 million years since the extinction of the non-Avian dinosaurs, the diversity of mammals has exploded to over 6000 species. Now there are mammal species, both nocturnal and diurnal, that have no natural predators. However, mammals have remained largely brown, gray and black.
This may be due to most mammals’ continued lack of color vision, he said Ted Stankowicha behavioral evolutionary ecologist at California State University, Long Beach. Scientists speculate that the mammals sacrificed someone color vision to get better night vision in the age of the dinosaurs. Most mammals still have dichromatic vision, meaning they only have two of the three types of cones that help the eye perceive color. Dichromats cannot see colors such as red, orange, turquoise and purple, and generally cannot see colors with as much saturation as trichromats, which have all three types of cones.
The purposes animals primarily use color for—attracting mates and other communication within their species, blending in with camouflage, and signaling to predators that they are poisonous or otherwise dangerous—do not work when their partner or predator cannot see the colors they use. Some mammals have actually used this lack of color vision to their advantage. For example, although tigers looks orange to our trichromatic eyes, they looks green to their mammalian preywhich makes them perfectly camouflaged among the grass when hunting.
Instead of using vibrant colors, Stankowich said, many mammals use patterns and contrasting colors, such as black and white or brown and yellow, to signal to each other. Skunks and polecats, for example, use black and white spots and stripes to tell predators they have a stinky trick up their sleeve. The African wild dogknown for its unique pattern, has a distinctive white tail that scientists believe is used for signaling while you are hunting. The Indian giant squirrelknown for its high-contrast black, reddish-brown and orange-yellow pattern, can use this as camouflage against various types of predators.
Because mammals have adopted new ways of color signaling, there may not be much of a reason for them to regain color vision. (The few mammals with trichromatic vision – primates, including humans and some monkeys – developed color vision too much special reasons.) Stankowich noted that the few mammals that show bright blue and red colors, such as baboons, golden monkeys, and mandrills, are also among the mammals with the best color vision.
Fluorescence and iridescence
Recent studies have highlighted some other exceptions. For example many mammal fluoresce under ultraviolet light, which the human eye cannot detect, but some other mammals can. Moreover, Jessica Dobsonan evolutionary biologist at Ghent University, and colleagues have discovered iridescence in a handful of mammalian species not previously known to have this shiny feature.
“It was a lightbulb moment,” Dobson said of this iridescent discovery, which occurred when she opened a museum drawer and sunlight hit the preserved skins of several tropical rat species at just the right angle. Dobson isn’t sure if these iridescent colors serve any evolutionary purpose, but she said it’s still exciting to know there are still mammalian color mysteries to unlock.
“When you start looking, mammals are more colorful than we give them credit for,” Dobson said.
