Industrially, a pigment is any finely divided insoluble black, white or colored solid material, a major function of which is to improve the appearance of or give color to the medium in which it is to be used.

Incorporation is always by simple physical mixing of pigment and medium, and it is this feature that distinguishes a pigment from a dyestuff.

Pigments and dyes are often derived from the same basic building blocks. The fundamental criteria that separates the two is that dyes are soluble in the media into which they are incorporated and pigments are not.
Given the large number of pigments and dyes available, a system of classification is necessary:

• The Color Index (CI). Within the CI system, each commercially available product is classified by the CI generic name which described the type of products it is.
• Each product has a CI generic name and number that summarizes its properties, e.g. Pigment Red 254.

In addition, where the chemical constitution of the products has been disclosed, it is also allocated a five-figure CI constitution number.