Chestnut-brown is a distinct and unique color that could be difficult to describe using antonyms. However, some contrasting colors that come to mind include stark white, icy blue, or jet black. These are colors that are at the opposite end of the spectrum, and when paired with chestnut-brown, they create a striking contrast. Other potential antonyms for chestnut-brown might include bright oranges, vibrant yellows, or vivid greens. Ultimately, the choice of antonyms will depend on the context in which chestnut-brown is used, and the specific effect the writer wishes to achieve. Nevertheless, there are plenty of color combinations and contrasts that can effectively offset the warm richness of chestnut-brown.