A big mess? Not necessarily. A distraction? Yes.
There was one band at the Edinboro PA Highland Games this year where everyone wore the same uniform - except one guy who wore a different tartan. And as much as I was concentrating on what they were playing, my attention kept going back to that guy - why wasn't he in the band uniform?

The only other examples I've seen were a band at the Fort Erie Celtic Festival a couple of years ago - half the band was pleated to sett, and the other half to stripe (there's a picture of that here somewhere); and again at Edinboro - the Erepa Grotto Shriners - their kilts were all the same, but the drummers wore red & white argyle hose, and the pipers wore red & black. One of those little details that registers in the back of your mind, and nags at you until you realize it.