What pigments do living things use, and why can so few animals make a blue one?

Melanins: made everywhere, limited to the dark end

Melanins are polymers built inside organelles called melanosomes. Eumelanin gives blacks and dark browns, pheomelanin gives rufous and yellowish browns, and the two mixed in different proportions cover the earth-toned range of mammal coats and many feathers. Melanin absorbs across the whole visible spectrum, more strongly at short wavelengths, so it cannot produce a saturated red, yellow, green or blue. Its usefulness goes beyond colour: it has a high refractive index, which is why stacked melanosomes serve as the reflecting layers in iridescent feathers, and feathers containing it are reported to resist wear better than unpigmented ones.

Carotenoids: eaten, then sometimes rebuilt

Animals cannot build carotenoids from scratch. The yellows, oranges and reds of flamingos, finches, goldfish and salmon flesh start as pigments made by plants, algae and microbes and pass up the food chain. Some are deposited unchanged. Others are chemically converted first: genetic work on red siskins and red-factor canaries implicates a cytochrome P450 enzyme, CYP2J19, as the ketolase that turns dietary yellow carotenoids into red ketocarotenoids. Binding to protein changes the colour again — the red carotenoid astaxanthin, held in the crustacyanin complex of a lobster's shell, looks dark blue, and cooking releases it as orange-red. That is the nearest most animals come to a blue made with pigment, and it is a red molecule in disguise.

Because the raw material is dietary, a captive flamingo fed without carotenoids moults into pale feathers. The colour records the last moult's diet, not today's.

Pigments animals make for themselves

Three further classes are synthesised in the body. Pterins give the whites, yellows and oranges of many butterflies' wings and the eyes and skin of various fish, amphibians and reptiles; a recent review places them between melanins and carotenoids — home-made like the first, bright like the second — and notes how little is known about their genetics. Parrots colour their red, orange and yellow feathers with psittacofulvins, a set of five pigments found in all 44 species surveyed and absent from the blood during feather growth, which points to manufacture at the feather itself. Turacos use turacin, a copper-containing porphyrin, for their crimson wing feathers: one of very few cases of a metal-based feather pigment.

Plant pigments and the anthocyanin–betalain divide

Plants make all their own pigments. Chlorophyll's green comes from absorbing red and blue light for photosynthesis. Carotenoids sit beside it in the chloroplast all season and give the yellow of autumn leaves once chlorophyll is broken down. Anthocyanins, dissolved in the cell sap, supply most reds, purples and blues of flowers and fruit and shift hue with acidity and with the metal ions and co-pigments bound to them. In beetroot, cacti and their relatives in the order Caryophyllales, betalains take the anthocyanins' place; a chemistry review reports that the two classes have not been found together in one plant. Plants, unlike vertebrates, do manage blue with pigment, by modifying anthocyanins rather than by any separate blue molecule.

Why animal blue is nearly always built, not dyed

The observation is firm: across fishes, amphibians, reptiles, birds and mammals, blue almost always turns out to be scattered light from nanostructure. The explanation is less firm. A blue pigment must absorb strongly in the red and yellow while passing blue, which requires a different kind of molecule from the melanins, carotenoids and pterins animals already have, and it has been proposed that structure was simply the more accessible route given that every animal already makes keratin, collagen, chitin or guanine. That is an argument about evolutionary accessibility, and it has not been tested in the way a mechanism can be.

The data

What the evidence says

Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.

• FactStrong evidence

  A survey by liquid chromatography of red feathers from 44 parrot species found the same five psittacofulvin pigments in all of them, and none in the birds' blood while feathers were growing, indicating synthesis at the feather rather than uptake from food.

  Source: Distribution of unique red feather pigments in parrots

• FactStrong evidence

  Birds make red feather pigments by converting dietary yellow carotenoids into red ketocarotenoids, and genome comparisons of red siskins, canaries and red-factor canaries implicate the gene CYP2J19 as the enzyme responsible.

  Caveat: The enzyme's role is inferred from introgression and expression data in these finches.

  Source: Genetic basis for red coloration in birds

• FactStrong evidence

  The red pigment of turaco wing feathers, turacin, is a copper complex of a uroporphyrin.

  Source: A reinvestigation of turacin, the copper porphyrin pigment of certain birds belonging to the Musophagidae

• FactStrong evidence

  Melanin has a high refractive index as well as broadband absorption, which allows melanosomes to act as optical building blocks in structural colours in addition to colouring tissue directly.

  Source: Melanosomes: biogenesis, properties, and evolution of an ancient organelle

• FactStrong evidence

  Betalains replace anthocyanins in most families of the order Caryophyllales, and the two pigment classes have not been found together in the same plant.

  Source: Biological Properties and Applications of Betalains

• Colourwise interpretationLimited evidence

  The rarity of blue pigment in animals is better described as an observed pattern than as an explained one: the suggestion that structure was the more accessible evolutionary route is plausible but untested.

  Based on: The review documents the pattern across vertebrate classes; Colourwise found no cited experiment or comparative analysis that tests why pigmentary blue did not evolve.

  Caveat: Absence of a test is not evidence against the suggestion.

  Source: On the blue coloration of vertebrates

Related questions

Why do flamingos lose their pink in captivity without supplements?

Their pink is carotenoid taken from food and laid into each feather as it grows. Without a dietary supply, the feathers grown at the next moult are pale. Greater flamingos also spread carotenoid-bearing preen oil on their plumage, which fades between applications.

Are a parrot's red and a cardinal's red the same pigment?

No. A cardinal's red is a carotenoid obtained from food and converted in the body. A parrot's red is a psittacofulvin, a different class of molecule that parrots make at the growing feather and that no other bird group is known to use.

Is the green of a turaco a pigment too?

Yes, and that makes turacos unusual. Most green feathers are structural blue over yellow pigment, but turacos carry a copper-based green pigment, turacoverdin, alongside the red turacin in their wings.

Why does a cooked lobster turn red?

The shell's pigment is astaxanthin, a red carotenoid. In the living animal it is held in a protein complex that shifts its absorption so the shell looks dark blue. Heat denatures the protein and the pigment returns to its free, orange-red colour.

Related topics

Go further

Sources

• Distribution of unique red feather pigments in parrots — Biology Letters 1, 38–43 (McGraw, Nogare) (Primary research)
• Genetic basis for red coloration in birds — Current Biology 26, 1427–1434 (Lopes, Johnson, Toomey and others) (Primary research)
• A reinvestigation of turacin, the copper porphyrin pigment of certain birds belonging to the Musophagidae — Proceedings of the Royal Society B 127, 106–120 (Rimington) (Primary research)
• Melanosomes: biogenesis, properties, and evolution of an ancient organelle — Physiological Reviews 99, 1–19 (D'Alba, Shawkey) (Academic)
• Biological Properties and Applications of Betalains — Molecules (MDPI) (Academic)
• On the blue coloration of vertebrates — Pigment Cell Research 20, 14–26 (Bagnara, Fernandez, Fujii) (Academic)
• Pterin-based pigmentation in animals — Biology Letters 17, 20210221 (Andrade, Carneiro) (Academic)
• Chemistry, Occurrence, Properties, Applications, and Encapsulation of Carotenoids—A Review — Plants (MDPI) (Academic)
• Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits — Food & Nutrition Research (Academic)
• Lobster colour change mystery solved — The University of Manchester (Academic)
• Selective bird predation on the peppered moth: the last experiment of Michael Majerus — Biology Letters 8, 609–612 (Cook, Grant, Saccheri, Mallet) (Primary research)
• Greater flamingos Phoenicopterus roseus use uropygial secretions as make-up — Behavioral Ecology and Sociobiology 65, 665–673 (Amat, Rendón, Garrido-Fernández and others) (Primary research)
• The color of greater flamingo feathers fades when no cosmetics are applied — Ecology and Evolution 11, 13773–13779 (Chiale, Rendón, Labaude and others) (Primary research)
• How Birds Make Colorful Feathers — Cornell Lab of Ornithology, Bird Academy (Academic)
• Plumage coloration is a sexually selected indicator of male quality — Nature 350, 337–339 (Hill) (Primary research)
• Carotenoid metabolism strengthens the link between feather coloration and individual quality — Nature Communications 9, 73 (Weaver, Santos, Tucker, Wilson, Hill) (Academic)
• What does carotenoid-dependent coloration tell? Plasma carotenoid level signals immunocompetence and oxidative stress state in birds – a meta-analysis — PLoS ONE 7, e43088 (Simons, Cohen, Verhulst) (Academic)
• A highly contiguous nuclear genome assembly of the mandarinfish Synchiropus splendidus (Syngnathiformes: Callionymidae) — G3: Genes, Genomes, Genetics 11, jkab306 (Stervander, Cresko) (Primary research)
• Why leaves turn red in autumn. The role of anthocyanins in senescing leaves of red-osier dogwood — Plant Physiology 127, 566–574 (Feild, Lee, Holbrook) (Primary research)
• Unravelling the evolution of autumn colours: an interdisciplinary approach — Trends in Ecology & Evolution 24, 166–173 (Archetti, Döring, Hagen and others) (Academic)
• Science of Fall Colors — USDA Forest Service (Official standard or government)
• The biology of color — Science 357, eaan0221 (Cuthill, Allen, Arbuckle and 24 others) (Academic)

Reviewed 6 October 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.