Buy the man some dockers! When I first met my hubby, he had NOTHING in between dress pants and jeans. I bought him his first pair of dockers and since realizing 1) they are as comfortable as jeans (if not more so), 2) he can wear it with a polo shirt (instead of short sleeved dress shirt) he actually started wearing them on his own without me asking him to. I think I know the greens you are talking about, my husband has a pair of those, and they are really kind of tough to match with things. Not quite neutral, if you know what I mean. Dockers/chinos in a light tan/putty/whatever color you call those are pretty easy to match. Tell him he will be a lot more comfortable in dockers than dress pants every night, especially with a tropical shirt.
And although I made the "overpack" comment, I would bring 7 shirts! Though really if you're talking dinners only, after formal and semi-formal nights, plus tropical night, that's only 4 other shirts. If they are polos that he might otherwise wear during the day, what I like to do is wear a fresh shirt for dinner the night before and then wear that all day long the next day (to get all sweaty and dirty) and repeat the next day with a clean shirt.
Lisa