Color Index is basically a compendium of dyes, that has a huge volume of data. It was prepared in the UK by the Society of Dyers and Colorists. In the USA by the American Association of Textile Chemists and Colorists. It is available both in the book form, and on CD as well. In this reference book there is a very specific system to identify individual dyes. A five digit number is assigned to each individual chemical that is used as a dye. Consequently individual dyes get identified with reference to their CI number only. For example when specifying a dye for use in any staining method the CI number must be always provided.

The color index also has a system to assign a specific name (CI Name) for each of the dyes, to avoid any confusion regarding chemicals. The name given is totally based upon the dye's mode of behavior, base color and action. This is followed by a number. To give an example, the CI name given for chromoxane cyanine R (CI 43820) is Mordant Blue 3. Thus, the CI name therefore gives a specific way to identify a dye. Although the CI name is used less often than the CI number, the CI name is as useful in identifying a dye for a particular staining method.

The following table illustrates the use of the Color Index for yellow Organic pigment