Orange is the colour between yellow and red on the spectrum of visible light. Human eyes perceive orange when observing light with a dominant wavelength between roughly 585 and 620 nanometres. In painting and traditional colour theory, it is a secondary colour of pigments, created by mixing yellow and red. It is named after the fruit of the same name.

The orange colour of carrots, pumpkins, sweet potatoes, oranges, and many other fruits and vegetables comes from carotenes, a type of photosynthetic pigment. These pigments convert the light energy that the plants absorb from the sun into chemical energy for the plants’ growth. Similarly the hues of autumn leaves are from the same pigment after chlorophyll is removed.

In Europe and America, surveys show that orange is the colour most associated with amusement, the unconventional, extroverts, warmth, fire, energy, activity, danger, taste and aroma, Protestantism, the autumn and Allhallowtide seasons, as well as having long been the national colour of the Netherlands and the House of Orange. It also serves as the political colour of Christian democracy political ideology and most Christian democratic political parties. In Asia it is an important symbolic colour of Buddhism and Hinduism.

Etymology
The colour orange is named after the appearance of the ripe orange fruit. The word comes from the Old French orange, from the old term for the fruit, pomme d’orange. The French word, in turn, comes from the Italian arancia, based on Arabic nāranj, derived from the Sanskrit naranga. The first recorded use of orange as a colour name in English was in 1512, in a will now filed with the Public Record Office.

Prior to this word being introduced to the English-speaking world, saffron already existed in the English language. Crog also referred to the saffron colour, so that orange was also referred to as ġeolurēad (yellow-red) for reddish orange, or ġeolucrog (yellow-saffron) for yellowish orange. Alternatively, orange things were sometimes described as red such as red deer, red hair, the Red Planet and robin redbreast.

Science

Optics
In optics, orange is the colour seen by the eye when looking at light with a wavelength between approximately 585–620 nm. It has a hue of 30° in HSV colour space.

In the traditional colour wheel used by painters, orange is the range of colours between red and yellow, and painters can obtain orange simply by mixing red and yellow in various proportions; however these colours are never as vivid as a pure orange pigment. In the RGB colour model (the system used to create colours on a television or computer screen), orange is generated by combining high intensity red light with a lower intensity green light, with the blue light turned off entirely. Orange is a tertiary colour which is numerically halfway between gamma-compressed red and yellow, as can be seen in the RGB colour wheel.

Regarding painting, blue is the complementary colour to orange. As many painters of the 19th century discovered, blue and orange reinforce each other. The painter Vincent van Gogh wrote to his brother Theo that in his paintings, he was trying to reveal “the oppositions of blue with orange, of red with green, of yellow with violet … trying to make the colours intense and not a harmony of grey”. In another letter he wrote simply, “there is no orange without blue.” Van Gogh, Pierre-Auguste Renoir and many other impressionist and post-impressionist painters frequently placed orange against azure or cobalt blue, to make both colours appear brighter.

The actual complement of orange is azure – a colour that is one quarter of the way between blue and green on the colour spectrum. The actual complementary colour of true blue is yellow. Orange pigments are largely in the ochre or cadmium families, and absorb mostly greenish-blue light.

Pigments and dyes
Minium and massicot are bright yellow and orange pigments made since ancient times by heating lead oxide and its variants. Minium was used in the Byzantine Empire for making the red-orange colour on illuminated manuscripts, while massicot was used by ancient Egyptian scribes and in the Middle Ages. Both were toxic, and were replaced in the beginning of the 20th century by chrome orange and cadmium orange.
Cadmium orange is a synthetic pigment made cadmium sulfide. It is a by-product of mining for zinc, but also occurs rarely in nature in the mineral greenockite. It is usually made by replacing some of the sulphur with selenium, which results in an expensive but deep and lasting colour. Selenium was discovered in 1817, but the pigment was not made commercially until 1910.
Quinacridone orange is a synthetic organic pigment first identified in 1896 and manufactured in 1935. It makes a vivid and solid orange.
Diketo-pyrrolo pyrolle orange or DPP orange is a synthetic organic pigment first commercialised in 1986. It is sold under various commercial names, such as translucent orange. It makes an extremely bright and lasting orange, and is widely used to colour plastics and fibres, as well as in paints.
Why carrots, pumpkins, oranges and autumn leaves are orange
The orange colour of carrots, pumpkins, sweet potatoes, oranges, and many other fruits and vegetables comes from carotenes, a type of photosynthetic pigment. These pigments convert the light energy that the plants absorb from the sun into chemical energy for the plants’ growth. The carotenes themselves take their name from the carrot. Autumn leaves also get their orange colour from carotenes. When the weather turns cold and production of green chlorophyll stops, the orange colour remains.

Before the 18th century, carrots from Asia were usually purple, while those in Europe were either white or red. Dutch farmers bred a variety that was orange; according to some sources, as a tribute to the stadtholder of Holland and Zeeland, William of Orange. The long orange Dutch carrot, first described in 1721, is the ancestor of the orange horn carrot, one of the most common types found in supermarkets today. It takes its name from the town of Hoorn, in the Netherlands.

Flowers
Orange is traditionally associated with the autumn season, with the harvest and autumn leaves. The flowers, like orange fruits and vegetables and autumn leaves, get their colour from the photosynthetic pigments called carotenes.

Foods
Orange is a very common colour of fruits, vegetables, spices, and other foods in many different cultures. As a result, orange is the colour most often associated in western culture with taste and aroma. Orange foods include peaches, apricots, mangoes, carrots, shrimp, salmon roe, and many other foods. Orange colour is provided by spices such as paprika, saffron and curry powder. In the United States, with Halloween on 31 October, and in North America with Thanksgiving in October (Canada) and November (US) orange is associated with the harvest colour, and also is the colour of the carved pumpkins, or jack-o-lanterns, used to celebrate the holiday.

Food colourings
People associate certain colours with certain flavours, and the colour of food can influence the perceived flavour in anything from candy to wine. Since orange is popularly associated with good flavour, many companies add orange food colouring to improve the appearance of their packaged foods. Orange pigments and dyes, synthetic or natural, are added to many orange sodas and juices, cheeses (particularly cheddar cheese, Gloucester cheese, and American cheese); snack foods, butter and margarine; breakfast cereals, ice cream, yoghurt, jam and candy. It is also often added to children’s medicine, and to chicken feed to make the egg yolks more orange.

The United States Government and the European Union certify a small number of synthetic chemical colourings to be used in food. These are usually aromatic hydrocarbons, or azo dyes, made from petroleum. The most common ones are:

Allura red AC (also known as E129, its official name in Europe).
Sunset Yellow FCF, Yellow 6, and Red 40, known as E110 in Europe, are dyes made from aromatic hydrocarbons from petroleum.
Tartrazine, also known as Yellow 5 and E102 in Europe. A dye used in soft drinks such as Mountain Dew, Kool-Aid, chewing gum, popcorn, breakfast cereals, cosmetics, shampoos, eyeshadow, blush, and lipstsick.
Orange B is an azo dye approved by the US Food and Drug Administration, but only for hot dog and sausage casings.
Citrus Red 2 is certified only to colour orange peels.
Because many consumers are worried about possible health consequences of synthetic dyes, some companies are beginning to use natural food colours. Since these food colours are natural, they do not require any certification from the Food and Drug Administration. The most popular natural food colours are:

Annatto, made from the seeds of the achiote tree. Annato contains carotenoids, the same ingredient that gives carrots and other vegetables their orange colour. Annato has been used to dye certain cheeses in Britain, particularly Gloucester cheese, since the 16th century. It is now commonly used to colour American cheese, snack foods, breakfast cereal, butter, and margarine. It is used as a body paint by native populations in Central and South America. In India, women often put it, under the name sindoor, on their hairline to indicate that they are married.
Turmeric is a common spice in South Asia, Persia and the Mideast. It contains the pigments called curcuminoids, widely used as a dye for the robes of Buddhist monks. It is also often used in curry powders and to give flavour to mustard. It is now being used more frequently in Europe and the US to give an orange colour to canned beverages, ice cream, yogurt, popcorn and breakfast cereal. The food colour is usually listed as E100.
Paprika oleoresin contains natural carotenoids, and is made from chili peppers. It is used to colour cheese, orange juice, spice mixtures and packaged sauces. It is also fed to chickens to make their egg yolks more orange.

Source From Wikipedia