Laconic;
if you place your cursor over the crew member you'll see a pop-up with a bunch of stats each one a "rating" of a number out of a total of 100. Use this as a guide to determine where he'd best be employed. For example, if I wanted a good gunner I'd check the roster (in port) and see which guys have high gunnery skills (i.e. gun rating stat = 50/100 or higher). Same logic for damage control team, I'll try and get guys with Mechanical/Electrical = ??/100 where the ?? is a high number therefore a high skill level.
The green bar next to each "team" increases with the amount of skill in that team.
This will also increase (I believe) as you gain experience (and survive) your patrols.
PS; during a mission, if one the guys gets injured (i.e. the AA gunner) and shows pink I'll scan the crew and try and find someone else who has decent gunnery stats and switch them. This keeps a decent guy on the guns plus hopefully lets the "injured" gunner recover.