Primary color facts for kids
Primary colors (or primary colours) are sets of colors that can be combined to make a useful range of colors. The primary colors are those which cannot be created by mixing other colors in a given color space.
For subtractive combination of colors, as in mixing of pigments or dyes for printing, the primaries normally used are cyan, magenta, and yellow, though the set of red, yellow, blue is popular among artists.
For additive combination of colors, as in overlapping projected lights or in CRT displays, the primary colors normally used are red, green, and blue.
Biological basis
Primary colors are not a fundamental property of light but are related to the physiological response of the eye to light (the way the eye works). For humans, three primary colors are usually used, since human color vision is trichromatic.
Fundamentally, light is a continuous spectrum of the wavelengths that can be detected by the human eye, an infinite-dimensional stimulus space. However, the human eye normally contains only three types of color receptors, called cone cells. Each color receptor respond to different ranges of the color spectrum. Humans and other species with three such types of color receptors are known as trichromats.
Additive primaries
Media that combine emitted lights to create the sensation of a range of colors are using the additive color system. Television is the most common use of this.
The additive primaries are red, green, and blue. Because of the response curves of the three different color receptors in the human eye, these colors are optimal in the sense that the largest range of colors — a gamut — visible by humans can be generated by mixing light of these colors. Additive mixing of red and green light, produce shades of yellow or orange. Mixing green and blue produces shades of cyan, and mixing red and blue produces shades of purple and magenta. Mixing equal proportions of the additive primaries results in shades of grey; when all three colors are fully saturated, the result is white. The color space that is generated is called the RGB ("red, green, blue") color space.
Subtractive primaries
Media that use reflected light and colorants to produce colors are using the subtractive color method of color mixing. In the printing industry, to produce the varying colors, apply the subtractive primaries yellow, cyan, and magenta together in varying amounts. Subtractive color works best when the surface or paper, is white, or close to it.
Mixing yellow and cyan produces shades of green; mixing yellow with magenta produces shades of red, and mixing magenta with cyan produces shades of blue. In theory, mixing equal amounts of all three pigments should produce shades of grey, resulting in black when all three are fully saturated, but in practice they tend to produce muddy brown colors. For this reason, a fourth "primary" pigment, black, is often used in addition to the cyan, magenta, and yellow colors.
The color space generated is the so-called CMYK color space. The abbreviation stands for "Cyan, Magenta, Yellow, and Black" — K stands for "Kohle" (German for coal) and is used to represent black as 'B' could be confused with 'Blue'.
In practice, mixtures of actual materials like paint tend to be less precise. Brighter, or more specific colors can be created using natural pigments instead of mixing, and natural properties of pigments can interfere with the mixing. For example, mixing magenta and green in acrylic creates a dark cyan - something which would not happen if the mixing process were perfectly subtractive. In the subtractive model, adding white to a color does not (in theory) change its hue but does reduce its saturation. In fact, adding white usually does change the hue slightly (this is known as the Abney effect), for example, adding white to red makes it slightly bluish, or pink.
Images for kids
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The emission spectra of the three phosphors that define the additive primary colours of a CRT color video display. Other electronic colour display technologies (LCD, Plasma display, OLED) have analogous sets of primaries with different emission spectra.
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A photograph of the red, green, and blue elements (subpixels) of an LCD. Additive mixing explains how light from these colored elements can be used for photorealistic color image reproduction.
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Color Mixing Guide, John L. King 1925, cover and plates describing yellow, red, and blue color mixing.
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The CIE RGB, CIE XYZ color matching functions and LMS cone fundamentals. The curves are all for 2° fields.
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Ewald Hering's illustration of the psychological primaries. Red/green and yellow/blue form opponent pairs (top). Each color can be psychologically mixed to make other colors (bottom) with both members of the other pair but not with its opponent according to Hering.
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The color scheme of François d'Aguilon, where the two simple colors of white (albus) and black (niger) are mixed to the "noble" colors of yellow (flavus), red (rubeus), and blue (caeruleus). Orange (aureus), purple (purpureus), and green (viridis) are each combinations of two noble colors.
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Johann Heinrich Lambert's "Farbenpyramide" tetrahedron published in 1772. Gamboge (yellow), carmine (red), and Prussian blue pigments are used the corner swatches of each "level" of lightness with mixtures filling the others and white at the top.
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Philipp Otto Runge's sketch showing bl (blue), g (yellow) and r (red) as the fundamental colors.
See also
In Spanish: Color primario para niños
