I have his first green grenadine gross a and am looking for another forest green. Would the forest green in wool challis be a good one? Would that be mainly fall/winter wear? He also has a forest green Oxford which may be more versatile, although the challis looks good too.
Any of the wool challis, oxford weave or diamond weave are good options. The wool challis is more of a fall / winter tie (though I think the color you describe is more of a fall / winter color too), but if you like it the best, get it. In all honesty, how many forest green ties does a man need for spring / summer? I'd think that one would be enough. It's a nice color but IMO not a staple that you can use a few of (like say blues, greys, burgundy, black), so you can experiment with seasonal weaves at an earlier point.