Brown color in science and nature

Brown is a composite color. In the CMYK color model used in printing or painting, brown is made by combining red, black, and yellow, or red, yellow, and blue. In the RGB color model used to project colors onto television screens and computer monitors, brown is made by combining red and green, in specific proportions. The brown color is seen widely in nature, in wood, soil, human hair color, eye color and skin pigmentation. Brown is the color of dark wood or rich soil. According to public opinion surveys in Europe and the United States, brown is the least favorite color of the public; the color is most often associated with plainness, the rustic and poverty.

The term is from Old English brún, in origin for any dusky or dark shade of color. The first recorded use of brown as a color name in English was in 1000. The Common Germanic adjective *brûnoz, *brûnâ meant both dark colors and a glistening or shining quality, whence burnish. The current meaning developed in Middle English from the 14th century.

Words for the color brown around the world often come from foods or beverages; in the eastern Mediterranean, the word for brown often comes from the color of coffee; In Turkish, the word for brown is kahve rengi; in Greek, kafé, in Macedonian, kafeyev. In Southeast Asia, the color name often comes from chocolate: coklat in Malay; tsokolate in Filipino. In Japan, the word chairo means the color of tea.

Brown in science and nature
Brown is a composite color, made by combining red, yellow and black. In the RGB color model, which uses red, green and blue light in various combinations to make all the colors on computer and television screens, it is made by mixing red and green light.

In terms of the visible spectrum, “brown” refers to high wavelength (low frequency) hues, yellow, orange, or red, in combination with low luminance or saturation. Since brown may cover a wide range of the visible spectrum, composite adjectives are used such as red brown, yellowish brown, dark brown or light brown.

As a color of low intensity, brown is a tertiary color: a mix of the three subtractive primary colors is brown if the cyan content is low. Brown exists as a color perception only in the presence of a brighter color contrast. Yellow, orange, red, or rose objects are still perceived as such if the general illumination level is low, despite reflecting the same amount of red or orange light as a brown object would in normal lighting conditions.

Brown pigments, dyes and inks
Raw umber and burnt umber are two of the oldest pigments used by man. Umber is a brown clay, containing a large amount of iron oxide and between five and twenty percent manganese oxide, which give the color. Its shade varies from a greenish brown to a dark brown. It takes its name from the Italian region of Umbria, where it was formerly mined. The principal source today is the island of Cyprus. Burnt umber is the same pigment which has been roasted (calcined), which turns the pigment darker and more reddish.
Raw sienna and burnt sienna are also clay pigments rich in iron oxide, which were mined during the Renaissance around the city of Siena in Tuscany. Sienna contains less than five percent manganese. The natural sienna earth is a dark yellow ochre color; when roasted it becomes a rich reddish brown called burnt sienna.
Mummy brown was a pigment used in oil paints made from ground Egyptian mummies.
Van Dyck brown, known in Europe as Cologne earth or Cassel earth, is another natural earth pigment, that was made up largely of decayed vegetal matter. It made a rich dark brown, and was widely used during the Renaissance to the 19th century It takes its name from the painter Anthony van Dyck, but it was used by many other artists before him. It was highly unstable and unreliable, so its use was abandoned by the 20th century, though the name continues to be used for modern synthetic pigments. The color of Van Dyck brown can be recreated by mixing ivory black with mauve or with Venetian red, or mixing cadmium red with cobalt blue.
Mars brown. The names of the earth colors are still used, but very few modern pigments with these names actually contain natural earths; most of their ingredients today are synthetic. Mars brown is typical of these new colors, made with synthetic iron oxide pigments. The new colors have a superior coloring power and opacity, but not the delicate hue as their namesakes.
Walnuts have been used to make a brown dye since antiquity. The Roman writer Ovid, in the first century BC described how the Gauls used the juice of the hull or husk inside the shell of the walnut to make a brown dye for wool, or a reddish dye for their hair.
The Chestnut tree has also been used since ancient times as a source brown dye. The bark of the tree, the leaves and the husk of the nuts have all been used to make dye. The leaves were used to make a beige or yellowish-brown dye, and in the Ottoman Empire the yellow-brown from chestnut leaves was combined with indigo blue to make shades of green.

Brown eyes
In humans, brown eyes result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed and in many parts of the world, it is nearly the only iris color present. Dark pigment of brown eyes is most common in East Asia, Southeast Asia, South Asia, West Asia, Oceania, Africa, Americas, etc. as well as parts of Eastern Europe and Southern Europe. The majority of people in the world overall have dark brown eyes. Light or medium-pigmented brown eyes are common in Europe, Afghanistan, Pakistan and Northern India, as well as some parts of the Middle East.

Brown hair
Brown is the second most common color of human hair, after black. It is caused by higher levels of the natural dark pigment eumelanin, and lower levels of the pale pigment pheomelanin. Brown eumelanin is more common among Europeans, while black eumelanin is more often found in the hair on non-Europeans. A small amount of black eumelanin, in the absence of other pigments, results in grey hair. A small amount of brown eumelanin in the absence of other pigments results in blond hair.

In Western popular culture, a common stereotype is that brunettes are stable, serious, smart and sophisticated. A British study into hair color and the intensity of attraction found that 62 percent of the men participating in the study associated brown-haired women with stability and competence. Brunettes were described as independent and self-sufficient by 67 percent of the men, and as intelligent by 81 percent.

Brown skin
A majority of people in the world have skin that is a shade of brown, from a very light honey brown or a golden brown, to a copper or bronze color, to a coffee color or a dark chocolate brown. Skin color and race are not the same; many people classified as “white” or “black” actually have skin that is a shade of brown. Brown skin is caused by melanin, a natural pigment which is produced within the skin in cells called melanocytes. Skin pigmentation in humans evolved to primarily regulate the amount of ultraviolet radiation penetrating the skin, controlling its biochemical effects.

Natural skin color can darken as a result of tanning due to exposure to sunlight. The leading theory is that skin color adapts to intense sunlight irradiation to provide partial protection against the ultraviolet fraction that produces damage and thus mutations in the DNA of the skin cells. There is a correlation between the geographic distribution of ultraviolet radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Darker-skinned populations are found in the regions with the most ultraviolet, closer to the equator, while lighter skinned populations live closer to the poles, with less UVR, though immigration has changed these patterns.

While white and black are commonly used to describe racial groups, brown is rarely used, because it crosses all racial lines. In Brazil, the Portuguese word pardo, which can mean different shades of brown, is used to refer to multiracial people. The Brazilian Institute of Geography and Statistics (IBGE) asks people to identify themselves as branco (white), pardo (brown), negro (black), or amarelo (yellow). In 2008 43.8 percent of the population identified themselves as pardo.

The thin top layer of the Earth’s crust on land is largely made up of soil colored different shades of brown. Good soil is composed of about forty-five percent minerals, twenty-five percent water, twenty-five percent air, and five percent organic material, living and dead. Half the color of soil comes from minerals it contains; soils containing iron turn yellowish or reddish as the iron oxidizes. Manganese, nitrogen and sulfur turn brownish or blackish as they decay naturally. Rich and fertile soils tend to be darker in color; the deeper brown color of fertile soil comes from the decomposing of the organic matter. Dead leaves and roots become black or brown as they decay. Poorer soils are usually paler brown in color, and contain less water or organic matter.

Mollisols are the soil type found under grassland in the Great Plains of America, the Pampas in Argentina and the Russian Steppes. The soil is 60–80 centimeters deep and is rich in nutrients and organic matter.
Loess is a type of pale yellow or buff soil, which originated as wind-blown silt. It is very fertile, but is easily eroded by wind or water.
Peat is an accumulation of partially decayed vegetation, whose decomposition is slowed by water. Despite its dark brown color, it is infertile, but is useful as a fuel.

Mammals and birds
A large number of mammals and predatory birds have a brown coloration. This sometimes changes seasonally, and sometimes remains the same year-round. This color is likely related to camouflage, since the backdrop of some environments, such as the forest floor, is often brown, and especially in the spring and summertime when animals like the snowshoe hare get brown fur.

The brown rat or Norwegian rat (Rattus norvegicus) is one of the best known and most common rats.
The brown bear (Ursus arctos) is a large bear distributed across much of northern Eurasia and North America.
The ermine (Mustela erminea) has a brown back in summer, or year-round in the southern reaches of its range.

The solid waste excreted by human beings and many other animals is characteristically brown in color due to the presence of bilirubin, a by-product of destruction of red blood cells.

Source From Wikipedia