The value notation is a measure of the amount of light that reaches the eye under standard lighting conditions. The actual amount of light that reaches the eye is related logarithmically to color value. These values may be designated for either achromatic or chromatic conditions. Thus, a card of the color chart for soil has a series of chips arranged vertically to show equal steps from the lightest to the darkest shades of that hue. Chroma is the relative purity or strength of the spectral color.
Chroma indicates the degree of saturation of neutral gray by the spectral color.
Figure 3-24 illustrates that color chips are arranged horizontally by increasing chroma from left to right on the color card. The complete color notation can be visualized from figure 3-24 . The darkest shades of that hue are at the bottom of the card and the lightest shades are at the top. Conditions for measuring color. The moisture content of the sample and the roughness of its surface affect the light reflected.