On the advice of some of the folks on this forum, I bought a copy of "So You're Going To Wear The Kilt", by J. Charles Thompson. It is pretty good, but one thing that Mr. Thompson says I found rather surprising. He says (on page 77 of my edition):

"This is one of the commonest mistakes made by American wearers of Scottish attire.
One sees pictures of Americans at Highland Games accompanying visiting chiefs from
Scotland. If the Scot has any tartan above the waist, it is the folded plaid laid over
the shoulder. The American will have an evening plaid fastened at the shoulder by a
"poached egg" brooch. The contrast is appalling. This time I am not expressing just
a personal opinion. If anyone cares to confirm it, I suggest that he write to someone
in Scotland who habitually wears the kilt. In my personal opinion (which anyone is
free to disagree with) the evening plaid is even too dressy to go well with the Prince
Charlie coatee. As I have said (and will say later at least once more -- sorry!), I like
to see the Prince Charlie kept as simple as possible, saving the plaid, jabot, and
dirk for full dress."

So is he right? What think ye? Is it a faux-pas to wear the evening plaid with less than full dress??