Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered one of the additive primary colors. On the HSV color wheel, the complement of green is magenta; that is, a purple color corresponding to an equal mixture of red and blue light. On a color wheel based on traditional color theory (RYB), the complementary color to green is considered to be red.

The word green is closely related to the Old English verb growan, “to grow”. It is used to describe plants or the ocean. Sometimes it can also describe someone who is inexperienced, jealous, or sick. In America, green is a slang term for money, among other things. Several colloquialisms have derived from these meanings, such as “green around the gills”, a phrase used to describe a person who looks ill.

Several minerals have a green color, including emerald, which is colored green by its chromium content. Animals such as frogs, lizards, and other reptiles and amphibians, fish, insects, and birds, appear green because of a mixture of layers of blue and green coloring on their skin. By far the largest contributor to green in nature is chlorophyll, the chemical by which plants photosynthesize. Many creatures have adapted to their green environments by taking on a green hue themselves as camouflage.

Culturally, green has broad and sometimes contradictory meanings. In some cultures, green symbolizes hope and growth, while in others, it is associated with death, sickness, envy, or the devil. The most common associations, however, are found in its ties to nature. For example, Islam venerates the color, as it expects paradise to be full of lush greenery. Green is also associated with regeneration, fertility and rebirth for its connections to nature. Recent political groups have taken on the color as symbol of environmental protection and social justice, and consider themselves part of the Green movement, some naming themselves Green parties. This has led to similar campaigns in advertising, as companies have sold green, or environmentally friendly, products.

Etymology and definitions

The word green is found in several colloquial phrases derived from these meanings: in golf, the region of grass around the hole is trimmed short and referred to as the putting green, or simply, the green. Someone who works well with plants is said to have a green thumb or green fingers, a physically-ill person is said to look green around the gills, and the word greenhorn refers to an inexperienced person. A company is said to be greenwashing if they advertise positive environmental practices to cover up environmental destruction. Green with envy highlights another emotional association, which William Shakespeare had first described as the "green-eyed monster" in Othello and The Merchant of Venice.