Soil Color and Redox Chemistry Activity Source: Soil Science Society of America. Adapted with permission. Are soils like M&Ms™? Yes! Typical soil colors are red, brown, yellow, or black. These colors are often not the color of the minerals in the soil but coatings of iron oxides (Fe203, FeOOH, and so on) or organic matter on particles. The minerals beneath are often quartz or feldspar, which are grey. To see how coating affects soil color, consider red M&Ms™. [Read More]