The black antlers are due to a combination of being wet, and what could have been lots of rubbing on old power line poles, or sappy trees that tend to give them color. This property is barbed wire all the way around, and because an old railroad line runs through it, is bi-sected by two barbed wire fences. All of the corner posts and stretch posts are recycled power line posts, which are heavily treated, and the treatment will stain. I know the hogs in the area use them for scratch posts, and will stain their coats from it. It is reasonable to suggest that the deer sometimes use them for rubbing posts, and stain their antlers. All four bucks are from the same small county- three from the same stand on the same 400 acres of land- and all of them have differently shaded antlers. They're the darkest that I've seen, but not as dark as in the pic, because they were wet from dew and rain then.
The rifle is a remington 700 mountain rifle in .270 win.