The current vote tally has the olive drab being the favorite, so that's what I'll go with.
Olive drab: 15 votes
Mexican camo: 10 votes
ACU: 1 vote
Now the question is whether to go with the first fabric (the large sample I draped over the covered wagon framework as a mockup), or the second fabric (the small sample). Both are almost exactly the same color (the dark green small sample is ruled out), but they're different fabrics.
The large sample is coated Cordura, which is a nylon fabric and has a very water-resistant urethane coating. It's fairly inexpensive, I can buy 10 yards for about $75 with shipping. It's als extremely strong and tear-resistant.
The small sample is Sunbrella fabric, which is acrylic and has a water-resistant impregnation on it that probably needs to be renewed every few years or so. Sunbrella is also a very strong fabric, although perhaps slightly less strong than Cordura.
The downside of the Cordura is that nylon fabrics can stretch a bit over time, and nylon is a little less resistant to UV exposure than acrylic. Probably the Cordura wouldn't stretch enough to affect the fit, but I do plan to tailor it fairly tightly, so I don't really want any stretch happening over time. The downside of the Sunbrella is mainly the price - 10 yards of it would cost about $220 (Sailrite is offering free shipping through May 5).
I'll probably go with the more expensive Sunbrella, although I can put off the decision until just before the free shipping expires
.