The appearance of a pigment can only be described exactly by using a well-tried color system. The data given in the list of pigments important to the artist are based on the German Industrial Standards color chart DIN 6164, which, in [p. 57] addition to the DIN numbers, also contains Ostwald numbers and the American Munsell renotation. The colors of the spectrum--each precisely defined by its wavelength--are called hues. Each hue is given a symbol made up of numbers and letters. The orange hues, for instance, lie between red and yellow on the Munsell color solid and range from 1YR to 10YR, while the blues, situated between blue-green and purple-blue, range from 1B to 10B. A second number denotes the value, i.e., the lightness or darkness, which ranges from o/[black] to 10/ [white]. The chroma, or saturation of the color is characterized by a third number, which starts at /0 [neutral gray] and progresses with increasing color purity. All colors, as well as black, white, and all intermediate grays, can be described by Munsell numbers.
Apart from a few exceptions, the values given in the following list of pigments [see the Pigments Folder in Materials and Methods, with Wehlte's contributions to the indiv. pigment documents] were not measured with instruments but were determined by visual comparison with the color chips in the DIN 6164 color chart. In the present edition Munsell renotation symbols were substituted for DIN color symbols by reading them from respective DIN color chip. Pigment samples to be observed were laid down with a water-soluble medium. This method of characterizing colors is quite adequate for the present purpose. Expensive, time-consuming measurements with special instruments were thus avoided. In several cases the appearance of a color is also described simply in plain language. Observations should be carried out in diffuse dayliht [color temperature approximately 6000° Kelvin]. [pp. 57-58]
[Wehlte, Kurt. The Materials and Techniques of Painting. Translated by Ursus Dix. New York: Van Nostrand Reinhold Company. 1975.]