What color card do our geographers use to test the color of soil a?

Mensel Soil Color Cards are standard color cards used to determine and describe soil color based on the Mensel Color System and Mensel Color Nomenclature, which are compiled by combining the characteristics of soil color. The Mensel color system is based on the three attributes of color, i.e., hue, color value, and chromaticity. Hue refers to the color presented by the object, i.e., the dominant spectral color,*** there are 10 basic hues, of which, 5 primary hues, i.e., R (red), Y (yellow), G (green), B (blue), P (purple); 5 secondary hues, i.e., YR (yellow-red), GY (green-yellow), BG (blue-green), PB (violet-blue), RP (red-purple). Then 4 grades are divided by 2.5, such as 2.5YR, 7.5YR, 10YR and so on. Color value refers to the relative brightness of the soil color, with no color (N) as the benchmark, the absolute black (ideal black) as 0, the absolute white (ideal white) as 10, divided into 0-10 from dark to bright equal points. Chromaticity refers to the relative purity or intensity of the spectral colors, divided into 0-10 from weak to strong, the higher the chromaticity, the more intense the color. The order of color naming is hue, color value, chromaticity, such as a soil hue is 2.5Yh, color value is 4, chromaticity is 6, then the nomenclature is 2.5YR4/6. The complete nomenclature of the soil color is the name of the color ten Mensel color naming, such as red-brown (2.5YR4/6), brownish-gray (10YR6/1), and so on. When used, a soil sample with a standard color scale of the card relative to each other, you can determine and record the soil color.