There are several synonyms that can be used in place of "nut brown." One option is "chestnut," which refers to the reddish-brown color of the outer shell of a chestnut. Another possibility is "mahogany," a rich, dark brown color with hints of red or orange. "Cocoa brown" is also a suitable alternative, describing a warm, deep shade of brown reminiscent of a freshly brewed cup of hot cocoa. "Hickory" can also be used as a synonym, representing a light to medium brown color with subtle variations. Lastly, "walnut brown" refers to the warm, earthy tones found in the natural grain of a walnut tree.