Buff-brown is an adjective that describes a warm, yellowish-brown color. The antonyms or opposite words for buff-brown include shades that are either lighter or darker in color. For instance, buff-brown's opposite would be a cool, dark color like navy blue, coal black, or charcoal gray. Other antonyms for buff-brown include porcelain white, frosty blue, ice-cold gray, silver or metallic shades. There are also brighter, warmer colors that can be antonyms of buff-brown, such as bright scarlet, vibrant orange, or sunny yellow. In short, buff-brown antonyms are any colors that differ in tone from the warm, yellowish color the word describes.