WRT to Black Watch tartan being universal, and therefore a disservice to the Regiment of the same name, I'd have to disagree.

The Black Watch guard the red hackle as the item that one has to earn by service, not the tartan. My advice is to not wear a red hackle unless one has earned it the hard way.

The same goes for maroon t-shirts around paratroopers. Not a good idea unless you're one of them.