Pergola slats

I built a pergola 6 years ago. The joist are nice and sturdy 2 bt 10's. The slats on top of them were 1x3 pine (or maybe it was 1x4, don't recall). I did not prime anyof it -- just slapped on exterior oli based paint.
The joist have been fine - the paint still looks good. However, the tops of the slats has pretty much lost all it's paint.
Now I want to take those slats off and put down some sort of synthetic wood like Trex or TimberTech. I'd like something as close to white as possible. Since it does not carry a heavy load (maybe snow loads), it doesn't have to be strong... It will be seen from the top and the bottom so the funny shaped stuff is not a good choice.
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