Black troops would presumably have different faces and hair from white troops. Some companies have done Black Regiments in metal and it's nice to have purpose made troops. Still in this small scale a paint conversion would work if necessary.
I submit that a better set would be US Army Black troops from the First World War. Black troops often served with French Divisions and were issued French weapons, Adrian helmets, and web gear, but they wore standard US Army uniforms. So they have a unique look.