All one has to do is look at old time black and white deer hunting photos with hunters in their then traditional red plaid mackinaw jackets and you can see, against color blind quarry like deer, they were pretty efficient camouflage. Used to be for late season bow hunting in scrub oaks, my favorite camo was an old pair of faded brown Carhartt coveralls. Deer eyes are not that hard to fool. Folks that regularly hunt wild turkey and waterfowl have it a lot harder, especially once those animals have been pressured, and you are calling them to a spot they are looking directly at. It's also a lot harder to get animals regularly into ranges of less than 40 yards such as when bow hunting, turkey hunting and waterfowl hunting, as it is getting a deer into rifle range. I always get a kick outta those hunting shows where the hunters are in full camo, complete with face pant, while sitting in an elevated blind and shooting at animals 150 yards or more away. Still, if it instills more confidence in them, it's a good thing. Just like turkeys and waterfowl tho, deer in heavily pressured areas are more prone to avoid things that stick out. I have the privilege to hunt different areas for deer.....heavily pressured public land and low access private lane. While one can walk within 100 yards of the deer out feeding in a food plot on the private land and while they are are alert, will not immediately run, deer on the public land, seeing a hunter walking 400 yards across the swamp, are already gone. I think many times, in our attempt to increase our deer herd and promote "let 'em go to let 'em gro" has dumbed down deer in many areas.
Again, military camo was designed to fool some of the better eyes in the animal kingdom and the consequences of it not being effective are worse than just missing the opportunity of getting a shot at a game animal. Think about it.