Munsell color system in the context of "Lightness"

Colorfulness, chroma and saturation are attributes of perceived color relating to chromatic intensity. As defined formally by the International Commission on Illumination (CIE) they respectively describe three different aspects of chromatic intensity, but the terms are often used loosely and interchangeably in contexts where these aspects are not clearly distinguished. The precise meanings of the terms vary by what other functions they are dependent on.

• Colorfulness is the "attribute of a visual perception according to which the perceived color of an area appears to be more or less chromatic (Any color that is absent of white, grey, or black)". The colorfulness evoked by an object depends not only on its spectral reflectance but also on the strength of the illumination, and increases with the latter unless the brightness is very high (Hunt effect).
• Chroma is the "colorfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears white or highly transmitting". As a result, chroma is mostly only dependent on the spectral properties, and as such is seen to describe the object color. It is how different from a grey of the same lightness such an object color appears to be.
• Saturation is the "colorfulness of an area judged in proportion to its brightness", which in effect is the perceived freedom from whitishness of the light coming from the area. An object with a given spectral reflectance exhibits approximately constant saturation for all levels of illumination, unless the brightness is very high.

As colorfulness, chroma, and saturation are defined as attributes of perception, they can not be physically measured as such, but they can be quantified in relation to psychometric scales intended to be perceptually even—for example, the chroma scales of the Munsell system. While the chroma and lightness of an object are its colorfulness and brightness judged in proportion to the same thing ("the brightness of a similarly illuminated area that appears white or highly transmitting"), the saturation of the light coming from that object is in effect the chroma of the object judged in proportion to its lightness. On a Munsell hue page, lines of uniform saturation thus tend to radiate from near the black point, while lines of uniform chroma are vertical.

A color term (or color name) is a word or phrase that refers to a specific color. The color term may refer to human perception of that color (which is affected by visual context) which is usually defined according to the Munsell color system, or to an underlying physical property (such as a specific wavelength on the spectrum of visible light). There are also numerical systems of color specification, referred to as color spaces.

An important distinction must be established between color and shape, as these two attributes usually are used in conjunction with one another when describing in language. For example, they are labeled as alternative parts of speech terms color term and shape term.