My personal favorite website (next to this one, of course): Kaiser's Bunker.
The site is probably the best reference tool on the web for soft headgear, and I have followed his color illustrations of headgear (both in feldgrau and dunkelblau) in creating the reference threads on this site.
Any budding KR soft-headgear collector should start here:
Kaiser's Bunker Imperial German Cloth Headgear Guide
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