I do not think we can become too dogmatic about "horizon blue", doing so brings out the historic preservationist, museum employee, living history & reenacting geek in me. I am not a textile expert by any means, nor an expert in WWI uniforms. However, having been a collector before, and having friends who have not only done some pretty in depth research, but have some pretty awesome, advanced collections, I think I can say a thing or two about it with a modicum of "cred".
I know of a young feller who creates true, museum quality replicas of WWI uniforms, and spent a summer in museums across France cataloguing, photographing, etc. French army uniforms and accoutrements. He told me, as an observation, that "horizon blue" ran the gamut from a sky blue, to violet, to purple, to blue, etc. This makes perfect sense to me as some friends of mine had undertaken a study of US Army sack coats during the ACW and looked at about a dozen originals held in the collection of the Smithsonian, US Army Collections, etc. They said if you could have a rainbow out of dark blue, that's what you'd get if you lined them all up side by side. After hearing about my acquaintances research trip to France, and his observations afterward, it only makes sense to me that there would be some variation, etc.
Just my two kopeks,
Warren
