Here's a trade secret I use for deck washes...
Find a gaming shop...you know, Warhammer, etc. Games Workshop sells acrylic based inks, browns, chestnut, black, and something called 'Flesh Wash'. I use these on my decks, thinned with a little water of course.
Acrylics are more forgiving than enamels, but are also more susceptible to damage, scratches, etc.
Either way, spray your deck color, allow it to dry, then spray a coat of Future Floor wax over it, and allow that to dry for 24 hours. Once that's done, you can use a wash of thinned ink (as I do) or a wash of thinned paint. I prefer inks because the pigment is part of the carrier, not suspended in a carrier like a paint wash. I get very good results, and a $3 jar of ink goes a long way. Beautiful thing is...if you mess up, a small brush with clean Windex will remove the ink completely, even if it's dried and appears to have stained the paint. It's very forgiving.
If you do go with wood, I use a Polly-Scale color called Concrete, it matches weathered teak quite nicely...a tan with a gray hue to it. To thin acrylics, I use a 50-50 mix of rubbing alcohol and distilled water. For enamels, lacquer thinner.
Jeff