Green is the color between blue and yellow on the spectrum of visible light, It is evoked by light with a predominant wavelength of roughly 495–570 nm. In the subtractive color system, used in painting and color printing, it is created by a combination of yellow and blue, or yellow and cyan; in the RGB color model, used on television and computer screens, it is one of the additive primary colors, along with red and blue, which are mixed in different combinations to create all other colors. The modern English word green comes from the Middle English and Anglo-Saxon word grene, from the same Germanic root as the words “grass” and “grow”. It is the color of living grass and leaves and as a result is the color most associated with springtime, growth and nature. By far the largest contributor to green in nature is chlorophyll, the chemical by which plants photosynthesize and convert sunlight into energy. Many creatures have adapted to their green environments by taking on a green hue themselves as camouflage. Several minerals have a green color, including the emerald, which is colored green by its chromium content. In surveys made in Europe and the United States, green is the color most commonly associated with nature, youth, spring, hope and envy. In Europe and the U.S. green is sometimes associated with death, sickness, or the devil, but in China its associations are very positive, as the symbol of fertility. Because of its association with youth, it is sometimes used to describe someone who is inexperienced. In the Middle Ages and Renaissance, when the color of clothing showed the owner’s social status, green was worn by merchants, bankers and the gentry, while red was the color of the nobility. The Mona Lisa by Leonardo da Vinci wears green, showing she is not from noble family; the benches in in the British House of Commons are green, while those in the House of Lords are red. Green is also the traditional color of safety and permission; a green light means go ahead, a green card permits permanent residence in the United States. It is the most important color in Islam. It was the color of the banner of Muhammad, and is found in the flags of all Islamic countries, and represents the lush vegetation of Paradise. It is also often associated with the culture of Gaelic Ireland, and is a color of the flag of Ireland. Because of its association with nature, it is the color of the environmental movement. Political groups advocating environmental protection and social justice describe themselves as 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.