According to Historynet, the official colors for Civil War uniforms were blue for Union and grey for Confederates, but the reality is they were often much more varied. In many cases, troops wore whatever clothes that were available.
Early in the war, many volunteers from both sides simply wore clothing they brought from home. While both armies issued more formal uniforms as the war progressed, supply problems in the South often led to soldiers resorting to wearing captured Union uniforms or allowing their grey uniforms to accumulate dust until they reached a nutty brown color. In some cases, the irregular uniforms standards led to confusion on the battlefield, spurring both surprise attacks and friendly fire incidents.