A bit of an enigma

Tores Tuesday.
Yes, I know that My postings are few and far between now. That is due to my injury, sorry.
This time I am posting a bit of an enigma, and I hope a member here might be able to solve it.
This is a german Dunkelblau (dark blue) officers hat, Schirmmütze. So, the old style hat. The top cockade is the imperial one. The bottom is a bit hard to identify, but it seems that the center has been red and the rest yellow. The hat was made in Freiburg. It has red piping and red cloth around the bottom part of the hat. So, no mystery there. However, and this is the enigma, around the red band there is a thin black stripe. What does that signify? Can anyone find out what that is? I suppose this hat is for a military officer?