Wearing good camo and stalking deer in the juniper covered ridges around the lower areas of the Pecos river, I have had deer see my movement from 40 or so yards and come to attention. Then, I stayed motionless as they have approached while looking for what moved. Many times I thought they had me spotted and the jig was up, only to realize they were looking 'through me' and not seeing me, as they kept looking around and sometimes passing by only yards away.
The same has happened with elk.
I have walked while hunting and wearing ASAT camo and had deer see movement and look at me. When I stopped moving, they would loose me and often go back to feeding if I stayed still.
Deer in the east texas woods are deathly afraid of camo and if the see it move they will quickly leave the area, with the knowledge they have trouble honing in on it. Yes, as someone previously said, deer in many areas where visibility is short, do their business while looking for the white of a face or hand in the forest. For that reason, while sneaking through woods, I wear a face net and don't move my arms much and move slowly while carrying my gun or bow down as low as I can. My best camo in the early part of the season in the pine and oak ridges and pin oak and gum bottoms is the dark green/ black dickies. Deer see me coming quite easily and from a distance, but they think it is a cow and don't pay attention until I am close enough to pick them up, if I am moving real slow and taking my time looking hard for movement ahead of me. Generally, it helps to be moving much slower than a traveling buck.
My brother and I, archery hunting, have had bull elk see us sitting and come to within 3 yards trying to figure out what we were. Don't expect that with a red emblem showing on a cap. Predator camo is great if you need to be close, but we have done well wearing grey wool rich pants at times. Carhart color has been good while calling elk.
I consider carhartt or grey to be camo in many hunting environments, as I do the wonderful dark tan thinsulate insulated Wranglers.
I have never had wild turkeys come close in the fall if I was sitting on a live oak limb in central texas while having bright colored fetching on my arrows. Even without movement and otherwise having total camo they have always nailed me. I have stalked and drilled a few though, with total camo.
Camo is not necessary if one is a great hunter, sits on a ridge and shoots a long way, is still and has an animal travel over him, or is real lucky, but it helps if it blends in to the environment and one is subject to Murphy's Law.
