Reliability of Soil Color Standards

Standardized color charts with the Munsell notation have been routinely used by soil scientists for >60 yr. In recent decades, modern technologies (such as digital colorimeters) have permitted further precision in the measurement of soil colors. Preliminary digital measurements of soil color chips indicated some notable discrepancies between reported and measured colors. A comprehensive investigation was launched to examine the quality of soil color standards that involved five laboratories across the country. The standards examined included current products from two manufacturers as well as products manufactured during the past 40 yr. A small portion of color chips on these standardized charts are manufactured with gloss or semigloss finish; when digital instruments that include the specular light component were used to measure these chips, large discrepancies in value and chroma were observed. However, chips with flat finishes had much lower mean deviation in Munsell value and chroma (value-chroma distance of 0.3 unit) and the mean deviation in Munsell hue was 0.6 unit. There were no practical differences in the color quality between manufacturers, and the Macbeth/X-Rite books published during the last 40 yr appear to be of comparable quality. Published Munsell soil color standards have been, and continue to be, of high quality. Although digital instruments that include the specular component of light may produce erroneous color measurements of materials with shiny surfaces, the fine particulate nature of soil materials produce minimal specular reflection so that digital colorimeters can be used to measure soil color without this concern.