Please educate a Brit.

You got it mate. Deer see yellow but green, red and orange appear as shades of grey, 50 shades of grey to be exact :)

The other factor to keep in mind is a lot of the hunting here in the USA is done on public land. I know most if not all of your hunting is a "permission". There is no telling how many people may be out in the woods hiking with a gun looking for a deer. 

 
My first post.
Greetings all.
Apparently apart from apes and ourselves mammals generally only detect the world of colour in shades of brown/grey although I was told that horses tend to see some blue.
Birds see the spectrum but also ultra violet so washing hunting gear with detergents that have colour enhancements means to a bird you stand out in a bright glow !
 
about 3years ago I bought
a orange camo coveralls with thinsulate liner . I was the laughing stock of the club for awhile .I can say that the orange in the camo has not affected My harvest of squirrels,rabbits,deer ,coyotes or bobcats .I live in eastern NC where most shots are 50 yards in or less due to very dense under growth .My thought is that motion and scent control are more important in hunting animals than the Orange required bylaw.the one exception is ducks and geese they will flare at the sight of orange .
 
Here in Ohio we only have to wear hunter orange during our deer gun seasons. Which are shotgun/ straight walled cartridge and muzzle loading seasons. I have one hunter orange jacket I wear that has black branches to help break up the solid orange that most guys wear. Deer seem to key into movement more that anything else, but if the don't smell you and are not sure what you are they will try to circle downwind to confirm any suspicions If I jump a deer and don't think it got a good look at me and know it didn't smell me I stop and watch my downwind side to see if they circle around. Orange is worn only to keep from getting shot from people who shouldn't be out hunting in the first place..
 
Where I am, "200 square inches" of hunter orange is a must (for my small game hunting, anyway); but orange camo (for whatever reason) is not permitted. I've read articles that support what others have already said regarding hunter orange not being any more visible than any other "earth tones" (to the animals). Any time I lose a shot on a squirrel, I'm certain it's not my orange hat, but instead my clumsiness in the underbrush that draws their attention. I have seen some videos from guys in the UK who hunt rats, and they say that the color blue stands out to rats like lights in the darkness. I don't know the "truth of science" behind that, but if I ever hunt rats, I won't be wearing blue jeans.