I wouldn't mind forest green in the summer. I mean, the color IS inspired by shaded trees in a forest. If you live where there's snow, you don't see leaves in the winter-- only evergreens. I would do a bit of a muted forest green, though. Not too bright, but dark enough to make him happy. I'd pair it with something earthy, if that's your style. OR something with the color of a flower. Think of plant stems- some of those are a darker green as well, not light.
You do not have to go with color "trends," since colors (unless they're crazy bio hazard neon green-brown-yellow, I don't even know HOW to explain it) all show up in nature somewhere. If you do nature-inspired colors, it could be a summer theme without actually being... a summer theme.
We narrowed our color choices down to 2-
Dark, forest green and medium-violet or,
Ocean Blue and moss.
We're leaning toward the first one. :-)
And our wedding will be in the summer season.