Just want to second that comment on reflectivity. I see my friend stalking in a HECS shirt, in Arizona, and it simply shines when his shoulder catches the sun. Likewise for a friend in Advantage camo, made of sunshirt, fishing shirt material. Even older cotton blend camo can wash out and reflect as if to appear nearly white, or real light gray. Had an old ASAT shirt that faded so much that it looked sort of off white and black, so not good in dark brown, gray thickets.
I am wearing wool as much as temperatures allow. Cotton over the nylon and polyester sunshirts, for same reason.
I also want to second the comment about movement and cover. I am getting real close, often, in khakis and t-shirts, wool shirt, and my peers are shooting wheelies at over 70 yards, saying that can not get closer...
my two cents.