Regardless of function, you do want your AK to look good or you wouldn't have gone with the plumb furniture.
The black sling isn't the way to go. Black, IMO, is too much overdone in today's tactical fashion scene. You can't really go wrong with OD since your LBE is OD. Personally, I'd recommend the tan though.
Tan, while contrasting to OD doesn't clash with OD. In fact, the tan sling will draw the eye along it to the plum-stocked AK. An OD sling will get lost amongst the straps of your LBE and while it will blend fine, it won't give the same effect that the contrasting tan will.
Also with your AK by itself the tan will look quite well with the plumb, and while it's leaning against a wall (or BMP-2) it will look just as good. The OD sling will just make it look like a rehab SAR with the Romy sling on it. Ask yourself, do you want your AK to look like a rehab Romy SAR?
You should go with a tan sling if you really want to look sharp.
Ross