I actually lightly spray painted my wraps. Did it from a distance with tan or brown and grey - I honestly don't remember. I think it was a khaki tan paint and they very lightly done with grey. They were slightly off white and I just kind of dusted them to make them more tannish grey.
Speaking of, this cracked me up and made me sympathize: "At this point fiddling with dye samples is like old times with this costume." Indeed!
As for using a coupler, I used one, too. I used a threaded coupler and glued it well in place (before I did this, it was a bit wobbly for me). I put mine under my wrap near the middle of the staff. It works fine, though I honestly rarely break down my staff because taking the wrap on and off and getting it right afterward is a pain. Also, at that coupling point, it honestly doesn't help me much. The two pieces are still too big to fit in my suitcase for far-away cons, so I'll still have to ship or get a bigger suitcase or add another coupler. I was actually just thinking about this the other day and wishing I had made mine break into three sections for travel purposes and just put the couplers on the uncovered part of the staff (well, one of them, anyway - the other could likely go near the bottom of the wrap). Because you're right. They would look like part of the staff. Not quite as accurate, but much more practical for the real world.
That said, I shipped to Dragon Con for the first time two years ago (missed last year - bummer), and it was the best thing ever. So no biggie. I can ship again.
And the double layer PVC thing does work. It's a bit of a trick to get it done, but it works fine.
1" PVC with the staff parts on it, then 3/4" PVC inside the larger pipe, but put something thin around the smaller pipe to make it fit super tightly (I used one layer of electrical tape).