One source of inspiration was the British battledress.
I was also looking at the Afrika Korps.
Why the Afrika Korps? Unlike most European combatants, Germany had very few colonial holdings so when they went to war in Africa they had to design everything from scratch. It was a useful crucible to determine what traditional uniform features they were using were worth keeping.
The first attempt included high lace-up boots, breeches and a sun helmet.
Experience in Africa produced radical changes in the uniform.
Ankle-length boots with trousers that could be bloused into them, or shorts, became commonplace.
So too did a long shirt which could be worn instead of a tunic (and also served as a nightshirt!).
The most distinctive uniform item, however, was the peaked Afrika Korps cap.
During my reading, I turned up the interesting piece of information that these caps were lined with red material.
Some green aircrew clothing has an orange lining. The idea is that if the crashed crewman wants to be seen rather than camouflaged he wears the item inside out.
If a similar idea was intended for the Afrika Korps cap, why red and not some other colour that might be more visible in desert conditions?