No pink panthers or green dogs? Why are mammals not as brightly coloured as birds and fish

Ever wondered why a peacock, one of the most beautiful birds, has unique shades of blue and green, or a parrot flashes neon shades, while a dog or cat sticks to earth tones? Mammals are mostly found in shades of rock browns, blacks, and whites, missing the vivid pinks, violets, and neons of lizards, birds, or fish.Evolutionary biologist Matthew Shawkey from Ghent University explains animals create colour via pigments in skin or coats, or structural tricks with nanoscale patterns on feathers and scales that bend light for iridescence. Mammals, however, depend solely on melanin, the one pigment giving colour to their skin, while lacking the complex hair structures needed for structural colour, as explained in a Live Science report.However, there are also some exceptions that prove the rule otherwise, mandrills flaunt red-blue rumps on bare skin, not fur; sloths get their green from algae, not pigments. Fur's simplicity blocks nanoscale patterns needed for the unique bright colour. Early mammals hid from dinosaurs as nighttime prey for over 100 million years. A 2025 Science study by Shawkey's team examined melanosomes or pigment structures in Jurassic-Cretaceous fossils and modern mammals, revealing that ancient tones looked like today's muted shades."Any bright color would have been selected against," Shawkey told Live Science, since darkness rewarded camouflage over bold appearances.After the dinosaur extinction 66 million years ago, mammals burst into over 6,000 species but held onto drab fur. Behavioral ecologist Ted Stankowich from California State University, Long Beach, links this to dichromatic vision as most mammals see with just two colour cones, missing reds, oranges, purples, and vibrant saturations that trichromatic birds or primates detect.This night-adapted appearance, developed under dinosaurs, lessens the need for flashy signals others can't fully perceive.Nocturnal life also constrained pigment diversity; unlike birds using carotenoids from food, mammals depend on melanin without such needs.