What color is associated with well-drained internal drainage?

The color brown is commonly associated with well-drained internal drainage in soils. This coloration typically arises from the presence of iron oxides, which occur when iron is oxidized in aerated conditions, leading to a stable soil environment that allows for drainage. In well-drained soils, organic matter decomposition progresses efficiently, contributing to the brown hue.

In contrast, other colors in the options point towards different drainage conditions. Rust or really brown might suggest some iron oxide presence but can also indicate potential fluctuations in moisture levels, while gray suggests poor drainage or anaerobic conditions where iron is reduced. Lastly, gray with mottles indicates fluctuating water levels, which is a sign of less than ideal drainage. Therefore, the presence of brown signifies a steady, well-drained system, confirming its association with good internal drainage.