As far as deer go (and elk as well), they are pretty much color blind and if you do not move you can be standing right in front of them and if the wind is in your favor and is blowing your scent away from them they will not detect you. I have had a doe and fawn approach me and proceed to bed in a patch of saw grass not more then 2 ft away from me as I sat with my back to a tree waiting for that big buck to come out from behind that tree (which he never did).
Attached is a photo of an Elk that approached us as we were resting in a gulley with our backs agains a small cliff face and the wind in our faces just outside the badlands. Lucky for him it was Turkey Season...
