Given the relative sparseness of the trees in your photo, the green looks more natural to me. The brown suggests dead leaves “smothering” the grass that would otherwise grow there, which might look better if the areas were more densely forested than that. Of course, the colour of the playing surface you’ll be placing the felt pieces on top of could also affect the matter at hand.
It is the eternal question isn’t it about trees and wargaming. This seems to be the route I am going down: felt marker to show boundaries with some trees thrown on to denote it as a forest area. I think in terms of storage this is going to be my friend right now. Also in terms of manipulating miniatures inside wooded areas.
Thanks for the feedback.