Hi qrak,
If I remember pre-war shoulder strap of the Gre.-Regimen Nr.2 was white with red cypher, for feldgrau uniforms the cypher was red but I'm not sure about the piping - if it was white or red.
In 1914 many units (Rekruten-Depot, Ersatz-Bataillons) in the Garrisons used old pre-war...