A color production system can usually be described by a small number of dimensions along which variations produce the full gamut of colors possible. By analogy, these dimensions thus describe a space within which all possible colors reside. For example, color monitors use varying strengths of the additive primaries (red, green and blue) to produce their full gamut. If one were to imagine these as physical dimensions, red would form one axis, green another, and blue a third. The space described would thus be a cube. Color spaces commonly used in computer graphics include RGB (using the red, green and blue additive primaries), CMYK (using the cyan, magenta, and yellow subtractive primaries, plus black), and HLS (hue,lightness and saturation,arranged in a double hexcone form). RGB describes well the colors produced by graphics monitors,CMYK describes the colors produced by most hardcopy devices and HLS describes the phenomenological characteristics of color.