Are they fittings tied-in to your ground system for the boat? Do you maintain your zincs? Have you noted that i) the zincs are working? (i.e., they do wear reasonably so you have to renew them?); and, ii) they are wearing away at whatever a normal pace is for you?
Brown isn't bad. Actually a surface patina of "green" on true "Bronze" fittings isn't bad (as long as it's from atmospheric oxidation).
Whose through-hulls did Hunter install? (Please not my adoption of the correct, archaic spelling ;^))) ) Your question about the material being "real" bronze; and, not (say), brass is a good one. What year was the boat manufacturered? Did you check with the factory (I know they changed control of the Hunter production.)
When you hauled the boat, did you look at the through- or thru-hull valves ;^))) from below? What was condition of what you could see of the valves? Did you lube them? Do they function smoothly?
Those are some of the differential questions that I'd ask.