Color

Last modified by TerraIndex TerraIndex on 2021/09/30 15:20

In the world of defining colors the Munsell color system is a color space that uses three properties of color to identify the color, namely hue (basic color), chroma (color intensity), and value (lightness). The USDA (United States Department of Agriculture) accepted this system as the official color system for defining soils. [1]

The Munsell color system works in three different dimensions as can be seen on the picture on the right. This means that colors have several boundaries on which defining can be very difficult. An advice is to buy a chart yourself to identify soils in the field. Further on this page the charts can be found and used, but the colors don’t exactly match. [2]

System and coding

This system is made up out of three independent properties of color which form a sphere when they are put together.

Hue (Degrees around horizontal circles)
Chroma (Radially outward on horizontal axis)
Value (Vertically varying from zero to ten)

Hue

The hue-circle is made up from five principal colors and 5 intermediate colors. The main and intermediate colors, and codes are:

Red (R)
Yellow-Red (YR)

Yellow (Y)
Green-Yellow (GY)

Green (G)
Blue-Green (BG)

Blue (B)
Purple-Blue (PB)

Purple (P)
Red-Purple (RP)

This gives the hue-circle 10 different steps. Every step is named like the abbreviation with the number 5, as can be seen in the picture on the right. To define intermediate colors the 10 steps consist of sub steps of 2.5 points. This means that the code of the color between 10R and 5YR, 2.5YR is.[3]

Hue image [source]

Hue image

Value

Value is about the lightness of a color. If the lightness is zero the color is black and with a lightness of 10 the color is defined as white. The colors in the middle of the hue-circle have no hue and are called neutral colors. This means for example the color in the middle of the value-axis is neutral gray.

Value image [source]

Chroma

Colors that have a hue are called chromatic colors. Chroma is measured on the plate radially from the middle of the chart. Chroma is related to saturation. With a high chroma the color looks more pure and less polluted with other colors. With a lower chroma the color looks more like a pastel version of the original color. The chroma coordinates are not limited to a specific value. The maximum of chroma varies per color. This phenomena has its origin in the limit of the human eye, for example are green and yellow better visible with high chroma and purple not, because this exceeds the visible spectrum.

Chroma image [source]

Colorfulness

There is a special classification for the fraction of colored particles inside a sand- or gravel fraction. Their description can be found in the table below.

Value	Description
Not colorful	The fraction consist for more than 99 percent of the volume of white, grey or transparent grains.
Medium colorful	The fraction consist for 90 to 99 percent of the volume of white, grey or transparent grains.
Strongly colorful	The fraction consist for less than 90 percent of the volume of white, grey or transparent grains.