Not sure about today but when I was in Naval Aviation the brown shoes were the aviation branch of the Navy. The black shoes were the permanently assigned shipboard sailors. The aviation officers wore green uniforms and brown shoes. The only enlisted personnel authorized to wear green uniforms with brown shoes were Chief Petty Officers. All other enlisted wore the regular black shoe uniform with the exception that the lower ranked airman wore green stripes on an otherwise blue of white uniform. The black shoes called us "Aerodales" and we just called them "Black Shoes". These terms quickly distinguished your departmental classification within the Navy.