the wedding color is turquoise and he's planning to wear a black shirt along with his black suit? will it look good? if not, what are other alternatives for the color of the shirt?
If he is in the the Mafia, then I guess that would be O.K. Just kidding, I think the poor guy should wear whatever. From that day forward, his wardrobe may not be of his own choosing.
I think a black shirt would look alright, but a white shirt may look better. He could also wear a turquoise vest with a white or black shirt to make the color really stand out.