And God saw every thing that he had made, and,
behold, it was very good.
Genesis 1:31
"It is important to distinguish between pigments that animals produce by themselves (e.g., melanin, pterins, ommochromes, bile pigments) and those that are foodborne (carotenoids).
*Among the pigments produced by animals, the most common are melanins. They are usually brown to black, but also range from yellow to reddish brown. They are found in association (or not) with other pigments, particularly in the hair of mammals, bird feathers, butterfly wings, and so forth.
*If melanin production should fail, the animal is white with red eyes (albinos). When melanins do not migrate into the hair or feathers, the animal has a white coat or feathering, but pigmentation of the eyes, the skin, and the legs is normal.
*Finally, excessive melanin production gives a black color or something close to it (e.g., rabbits, dogs, hamsters, cats, panthers). Butterflies have very different colors on account of various pigments, in particular, pterin and ommochromes.
*Animals cannot produce carotenoids. Those they do possess have been eaten and often processed by the body. Birds are particularly capable of performing the processing of carotenoids. Many of them exhibit very diverse colors from yellow to red: goldfinch, robin, tit, chaffinch, and so forth. *As for the pink flamingo, its color exclusively arises from its diet, which consists mainly of planktonic crustaceans that feed on algae which are rich in carotenoids converted to red astaxanthin and canthaxanthin.
*Note that contrary to plants, the presence of blue and green pigments is exceptional in animals. Some rare butterfly wings contain such pigments. In most cases, the blue is of a structural type, as we shall see below. As for the green, it most often results from a blue structural color superimposed over the yellow of a pigment. This is particularly true for the skin of frogs and the green feathers of birds.
The blue color of feathers deserves special attention because it is not due to blue pigments and the colors do not change according to the observation angle, unlike the wings of Morpho butterflies. Therefore, there is no iridescence. Another physical phenomenon is actually involved: Light scattering by structural elements of very small size (several tens of nanometers) that constitute the
feather barbs.
For a long time, it was thought that the color was due to Rayleigh scattering (i.e., light scattering by particles with sizes less than one-tenth of the wavelength of light), a phenomenon responsible in particular for the blue color of the sky. However, this explanation is insufficient for bird feathers, as electron microscopy reveals that the feather barbs are made of keratin and air nanostructures with some partial order. Thus, constructive interferences occur locally without iridescence (i.e., without color changes depending on the observation angle) because there is no order over long distances. The interference reinforces the intensity of the scattered light at certain wavelengths that depend on the size and spacing of the elements that make up the nanostructure. It is, therefore, clear in this case that it is coherent light scattering." ChemistryView
"It is important to distinguish between pigments that animals produce by themselves (e.g., melanin, pterins, ommochromes, bile pigments) and those that are foodborne (carotenoids).
*Among the pigments produced by animals, the most common are melanins. They are usually brown to black, but also range from yellow to reddish brown. They are found in association (or not) with other pigments, particularly in the hair of mammals, bird feathers, butterfly wings, and so forth.
*If melanin production should fail, the animal is white with red eyes (albinos). When melanins do not migrate into the hair or feathers, the animal has a white coat or feathering, but pigmentation of the eyes, the skin, and the legs is normal.
*Finally, excessive melanin production gives a black color or something close to it (e.g., rabbits, dogs, hamsters, cats, panthers). Butterflies have very different colors on account of various pigments, in particular, pterin and ommochromes.
*Animals cannot produce carotenoids. Those they do possess have been eaten and often processed by the body. Birds are particularly capable of performing the processing of carotenoids. Many of them exhibit very diverse colors from yellow to red: goldfinch, robin, tit, chaffinch, and so forth. *As for the pink flamingo, its color exclusively arises from its diet, which consists mainly of planktonic crustaceans that feed on algae which are rich in carotenoids converted to red astaxanthin and canthaxanthin.
*Note that contrary to plants, the presence of blue and green pigments is exceptional in animals. Some rare butterfly wings contain such pigments. In most cases, the blue is of a structural type, as we shall see below. As for the green, it most often results from a blue structural color superimposed over the yellow of a pigment. This is particularly true for the skin of frogs and the green feathers of birds.
The blue color of feathers deserves special attention because it is not due to blue pigments and the colors do not change according to the observation angle, unlike the wings of Morpho butterflies. Therefore, there is no iridescence. Another physical phenomenon is actually involved: Light scattering by structural elements of very small size (several tens of nanometers) that constitute the
For a long time, it was thought that the color was due to Rayleigh scattering (i.e., light scattering by particles with sizes less than one-tenth of the wavelength of light), a phenomenon responsible in particular for the blue color of the sky. However, this explanation is insufficient for bird feathers, as electron microscopy reveals that the feather barbs are made of keratin and air nanostructures with some partial order. Thus, constructive interferences occur locally without iridescence (i.e., without color changes depending on the observation angle) because there is no order over long distances. The interference reinforces the intensity of the scattered light at certain wavelengths that depend on the size and spacing of the elements that make up the nanostructure. It is, therefore, clear in this case that it is coherent light scattering." ChemistryView
