The concept of a color gamut is widely used in applied colorimetry and printing technology. Characterization and adjustment of the color reproduction of printing devices is closely related to the uniformity of the color description throughout the body of the color gamut, as well as, to the calculation of the color difference. The difference also depends on how uniform the basis is. The CIE Lab color space is uneven. Despite the fact that many formulas for the color difference have been proposed to account its unevenness, there are areas in the gamut body that are difficult to describe. For a more complete understanding of this phenomenon, we introduce the concept of density of the Lab color space. The paper describes the concept of density and gives the first ideas about it.