Graycoat in the Civil War

REB

["This soldier fought under leaders like Lee and Jackson, often wearing a butternut-dyed uniform due to shortages. Think three-letter abbreviation for their side."]

During the Civil War, Confederate soldiers were often called "graycoats" because of their gray uniforms, while Union troops wore blue. The clue is a straightforward reference to this nickname, with "REB" being a common short form for "Rebel," another term for Confederate soldiers. It’s a direct historical reference without any hidden wordplay or tricks.