Seriously, I wear a dark suit, the band wears their uniforms without the gauntlets. If I had the band wearing full concert black (meaning wearing a dinner jacket...not just tux shirt & bow tie, I would still wear a suit in that case), then I would use a tux.
Your mileage may vary.
: What do you wear for UIL Concert and
: Sightreading? Suit? Tux? Swim suit?