To make or become more brown.
To cause to contain more racially 'brown' people, elements, or culture.
To become brown due to increased levels of humic material.
To become or make brown; to brown.
To make (something) brown; to brown.
To make (something) dark or dusky (“having a rather dark shade of colour”); to brown, to darken.
To become or make dark or dusky; to brown, to darken.