COLOR VARIABLES.--Colors vary in CHROMA, or freedom from admixture of white light; in BRIGHTNESS, or luminosity; and in HUE, which roughly corresponds to the mean wave length of the light emitted. COLORS, COMPLEMENTARY.--Those pairs of color which when mixed produce white or gray light, such as red and green-blue, yellow and indigo-blue, green-yellow and violet. COLORS, PRIMARY.--The red, green, and violet light of the spectrum, from the mixture of which all other colors can be produced. Also called fundamental colors. DYESTUFFS.--In commerce, any dyewood, lichen, or dyecake used in dyeing and staining. ELECTRIC LIGHT.--Light produced by electricity and of two general kinds, the arc light and the incandescent light. In the first the voltaic arc is employed. In the second a resisting conductor is rendered incandescent by the current. ENAMEL.--In the fine arts a vitreous substance or glass, opaque or transparent, and variously colored, applied as a coating on a surface of metal or of porcelain. GRATING, DIFFRACTION.--A series of fine parallel lines on a surface of glass, or polished metal, ruled very close together, at the rate of 10,000 to 20,000 or even 40,000 to the inch; distinctively called a diffraction or a diffraction grating, much used in spectroscopic work. GRAY.--A color having little or no distinctive hue (CHROMA) and only moderate luminosity. GREEN.--The color of ordinary foliage; the color seen in the solar spectrum between wave lengths 0.511 and 0.543 micron. EMERALD GREEN.--A highly chromatic and extraordinarily luminous green of the color of the spectrum at wave length 0.524 micron. It recalls the emerald by its brilliancy, but not by its tint; applied generally to the aceto-arsenate of copper. Usually known as Paris green. HIGH COLOR.--A hue which excites intensely chromatic color sensations. +HUE.--Specifically and technically, distinctive quality of coloring in an object or on a surface; the respect in which red, yellow, green, blue, etc., differ one from another; that in which colors of equal luminosity and CHROMA may differ.+ INDIGO.--The violet-blue color of the spectrum, extending, according to Helmholtz, from G two-thirds of the way to F in the prismatic spectrum. The name was introduced by Newton, but has lately been discarded by the best writers. LIGHT.--Adjective applied to colors highly luminous and more or less deficient in CHROMA. LUMINOSITY.--Specifically, the intensity of light in a color, measured photometrically; that is to say, a standard light has its intensity, or _vis viva_, altered, until it produces the impression of being equally bright with the color whose light is to be determined; and the measure of the _vis viva_ of the altered light, relatively to its standard intensity, is then taken as the luminosity of the color in question.