Oh, and I'd lose the black kilt. Wear the Murray tartan.
***. Wearing a black kilt just because it's a "tails" type of event seems like an attempt to Saxonize the kilt.

This being a United Nations ball, you may run into actual Scotsmen there. Do them proud, and wear the kilt according to their tradition! And besides, people from all other nations who are present will likely recognize the kilt more readily in its original context.