The problem with camo is that it appears in two places. First, it appears in wide open rolling moors in Scotland, as a man on the moor would possibly be seen at a good distance. So the game keepers, called ghillies would wear clothing suited to help them blend into the countryside so that poachers would approach quite close and could be caught. Hence the name ghillie suit for the modern sniper's garb.
The idea doesn't get applied outside of Scotland until the invention and wide spread use of telescopic sights on rifles that use smokeless powder (WWI), allowing snipers to hunt each other. Until that time, the sniper could just stand off and shoot with peep sights or standard sights at formations of men, until they spotted the puffs of smoke and all shot back at the sniper.
In the AWI no telescopic sights, and no rolling moors so no cammo. Chances were in North America that when you saw the enemy..., you were well within rifle range, and probably within musket range.
Morgan's rifle corps wore white hunting frocks. Indians used lots of red in their body paint. YET..., they tended to go unnoticed in the woods.
Having spent probably a couple thousand hours on this very subject in my first profession, and been amazed many times, it comes down to this...,
The human eye sees things in specific order. That order can be less than one second, but it does see in order..., movement, outline, color. IF you don't move fast, and if the outline is marred by natural foliage, differing light levels (shade and light), then the color doesn't matter all that much. We placed a man in blue jeans and red flannel shirt in the woods in heavy foliage, but he could be seen 100 yards away..., he didn't move and folks didn't see him, even when they walked within about ten yards... I have seen similar stuff time and time again.
The other thing is the face. A nice, white face, is a good way to get spotted and shot. Indians painted their faces red/black other colors, and most frontier guys had hats with brims (shaded the face). Again, when you do spot somebody, you are very very close. Remember the tactics then too, as they did and they applied them..., a man with a single shot weapon and a 'hawk does not want to get real close to an approaching enemy group, so will move (or get caught and be dead). A group of men with single shot weapons can stay put. When the firing starts camo would be a moot point as the smoke gives the shooter's position away.
LD