Highland musicians didn't wear reverse coloured coats. They wore the same red ones as everyone else in the regiment. The only exception was the band leader, who wore a white coat. The coats were all white with no facing colour in the usual places, but all the lace (and the fuzz on the wings) was in facing colour.
Sometimes the regular musicians are recorded in white coats, too. Not always, though.
I based 79th on the Mont St. Jean website, which had musicians' coats green. I did see most bagpipers wearing standard sergeant clothes in pictures and paintings, but I thought this would add more to the game's variety of uniforms, rather than having almost every single line infantry Brit wearing red.
I was also in doubt with the officers' pants. I know they weren't supposed to wear kilts, but idk if they should keep the vainilla ones or have the boots with the white pompoms and dark grey pants.
(I still don't know what's breeches and what's trousers ingame, so bear with me)
Why is the Pipe Major's rank insignia messed up?
Idk, I tried fixing it multiple times, and only succeeded at failing. As far as I know, it's an animation screw-up.
I'll see what I can do for the next patch.