The principal color is derived from the light that has penetrated and which, after being reduced by absorbing effect of the medium, is reflected by the second and third surface. Most colors are due to preferential absorption. The reflection from most surfaces is practically colorless. The principal color is derived from the light that has penetrated and which, after being reduced by the absorbing effect of the medium, is reflected by the second and third surface. The major factors influencing brightness are roughness, moisture, and organic matter.
Reflectance varies inversely with increasing roughness, organic matter content, and soil moisture.
The main contributors to curve form variations include mineralogy, organic matter, and over certain portions of the spectrum, moisture. 4.4 Moisture Soils generally become darker when wet as a result of a decrease in reflected energy in the visible part of the spectrum. All of these are due to overtones and combinations of the three fundamental vibrational frequencies of the H2O molecule . If you get sharp bands at 1.4 m and 1.9 m, the water is located in well-defined, ordered sites while if the bands are broad then the water is relatively unordered, as in soils. The important constituents of organic matter in soils are the humic and fulvic acids along with decomposing plant residues in various stages of decomposition.