In the Munsell system, body colours are arranged according to the criteria of brightness, hue and saturation to produce a complete sample catalogue in the form of a three-dimensional matrix. Brightness here refers to the reflectance of a body colour; the hue refers to the actual colour, while the term saturation expresses the degree of coloration, from the pure colour down to the uncoloured greyscale. Whereas a two-dimensional diagram is sufficient for colours of light, a three-dimensional system is required for body colours due to reflectance.