The most obvious property when looking at soil is its color. The color of soil can tell scientists a lot about it. Geologist officially recognize over 170 different soil colors. Most of these are shades of black, brown, red, gray, and white.
Generally speaking, the darker a soil is, the more nutrient rich it is. The darker color often indicates an increase in decomposed organic matter known as humus.
Gray soils often indicate poor drainage, while red soils can indicate very poor soils.
These general rules about soil colors can, however, be misleading. Under certain conditions, a very poor soil can appear as dark black, while a rich healthy soil can appear as red.