Why aren’t mammals as colorful as reptiles, birds, or fish? Most mammals exhibit brown and black fur because they lack the necessary pigments and structural components to produce vibrant colors, unlike birds and fish. This is largely due to relying on a single pigment, melanin, and the simple structure of their fur, which limits color expression. Their evolutionary history as nocturnal prey animals also favored camouflage over bright coloration.

• Mammals primarily have brown and black fur due to a lack of pigments and structures that create vibrant colors in other animals.
• Color expression in animals occurs through pigments within the body or structural coloration involving nanoscale patterns.
• Mammals mainly utilize melanin, a single pigment, for their coloration, with its absence creating white areas.
• The structure of mammal fur is too simple to produce the nanoscale patterns necessary for structural coloration.
• An evolutionary hypothesis suggests that early mammals, living as nocturnal prey to dinosaurs, favored camouflage with darker colors.
• Fossil evidence indicates ancient mammals were also shades of brown or gray.
• Most mammals have limited color vision, affecting how they use color for mating, communication, and camouflage.
• Some mammals use patterns and contrast (e.g., black and white) for signaling, and certain species display fluorescence or iridescence.
• Exceptions like mandrills and sloths (with algae) have vibrant colors on non-furry parts or due to external factors.