Dress code: Cocktail party attire; elegant but no black tie. Kilt equivalent?

[creagdhubh]

Cocktails?
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Absolutely smashing, Sandy!

[creagdhubh]

Not to take anything away from Steve or Matt, but charcoal grey and dark blue kilt jackets like they're wearing appear in The Highlanders of Scotland and thus have been around for at least 150 years.

Here both of them are, in one painting no less.

Extremely versatile colours. Same goes for the jacket and waistcoat in which Sandy (JSFMACLJR) is wearing.

[OC Richard]

Seems like the traditional jacket code is

tweed (in any colour, plain or pattern) = Outdoor Dress/Day Dress

Barathea or velvet (in any colour, and including kilting tartan) = Evening Dress

But you can easily come up with things which seem to blur the line, such as fine-woven black, charcoal, or navy blue tweed, or charcoal, navy, dark blue, or dark green Barathea, when used in a Day-cut jacket (Argyll jacket).