Given the period of the original photo, my guess is that his shoulder straps are blue (hellblau) with a red cypher and crown. The shoulder strap plate chart shown above is from a very specific time frame. The regiment's cypher was introduced on August 20, 1898. At that time, the regiment was in the XI Armee Korps and the strap was red with a yellow cypher and crown (as above). Seven months later the regiment was transferred to the XVIII A.K. and along with that they changed their straps to blue.