achromatic - Without color so that it ranges from black to white through various shades of gray.

black - The color that in theory absorbs all of the light falling onto it. This is very hard to achieve in practice although carbon black comes very close.

brightness - Attribute of a visual sensation according to which an area appears to emit more or less light.

Cartesian coordinates - A way of describing a position in space related to its distance from three intersecting planes that are perpendicular to each other and pass through a single point, the origin. These coordinates resemble a cube with the coordinates being the lengths of the sides.

chroma - Attribute of a visual sensation that permits a judgement to be made of the degree to which a chromatic stimulus differs from an achromatic stimulus of the same brightness.

chromaticity diagram - A picture of the possible range of color appearances that can be produced at a specific value or intensity level.

CIE - Commission Internationale de l'Eclairage. An international collaboration that has existed for 100 years to bring standardisation to the field of color. It has defined the average human visual response, several standard illumination sources and the mathematical relationship between many models describing color perception.

color - The range of light to which the normal human eye responds. These are the same colors that appear in a rainbow although there can also be mixtures.

color space - The range of light to which the eye is responsive. This allows a variation in value (intensity), in hue (color appearance) and saturation (chroma or how far it is from a grey scale). A color space should allow an observer to consistently evaluate color differences.

cylindrical coordinates -  A way of describing a position in space related to how far it is above the base of a cylinder, how far it is from the central axis and how far it is rotated around the circlar cross-section of the cylinder.

dye - A water soluble substance used to color material from an aqueous solution.

electromagnetic radiation - Energy that travels through space in the form of interacting electric and magnetic energies. All objects emit a wide range of electromagnet radiation and the eye is only sensitive to a small fraction of it, termed the visible spectrum. Some animals are able to detect radiation outside the visible spectrum, either in the infra-red (heat or longer wavelength) or in the ultra-violet (shorter wavelength).

gamut - The part of the complete 3-dimensional color space that can be observed. Different media have a gamut smaller than the gamut detectable by the human eye. Television, or monitors, generate color by combining light at different intensities that is emitted by spots of blue, green and red phosphors. Printed color images create color by varying the quantity of deposited magenta, cyan, yellow and black pigment or dye.

hue - A partial description of a color by describing where in the visible spectrum it appears to fall. By using the wavelengths that correspond to the range of colors seen in a rainbow, red to yellow  to green to blue, or a mixture of red and blue, the hue is constrained to fall in the range 0 degrees to 360 degrees as it moves continuously around a circle.

illumination - The quantity of light that falls onto an object. This varies according to the distance from the light source and the type of light source, its temperature, and its means of generating light in the visible spectrum. An illuminant is specified by the relative power distribution across the wavelenths of the visible spectrum. Standard sources include D65, daylight as represented by a black body radiator operating at 6500 degree Kelvin, and the F series that represent various fluorescent sources.

lightness - Attribute by which a perceived color is judged to be equivalent to one of a series of greys ranging from white black. (CIE International Lighting Vocabulary).

pigment - A water insoluable material dispersed in the material it colors.

pixel - An abbreviation for "picture element". It is the smallest addressable element of a display device. At any location on a screen there are three phosphor dots, red, green and blue whose relative intensities are varied to produce the desired color appearance. In printing it is created by the superposition of deposits of several pigments.

perceptual color - This is the chromatic interpretation of the color signals received by the brain. It is effected by the spatial environment surounding the specific object, the overall luminance levels, the light adaptation of the eye, and the human expectation of what is being viewed. This can lead to many optical illusions. 

saturation - The colorfulness of an object judged relative to the light intensity falling on it. Within the range of normal color vision an object will retain the same saturation as the light level is changed since both the chromaticity and the lightness change as the level of light is changed. 

value - Describes how the quantity of light reflected from an object compares to that reflected by black (0%) and that reflected by white (100%). This is a term used in the art environment and can also be called relative brightness.

wavelength - An accurate way of describing the hue of a color. Any pure color from the visible spectrum can be defined by its wavelength which is the physical distance between successive peaks in the waveform.