[PAR35]

He was accompanied by a lady (his wife, I’m guessing, but I don’t know) wearing the British flag, suggesting that was the actual theme of their costumes.

Well, it was a 4th of July event. Perhaps the theme was "Countries that have fought the US".

[naturalman1975]

The theme of the dinner was ‘Red, White, and Blue’, and people were asked to wear costumes revolving around that theme.

While the theme does seem to have been chosen because of the date, it wasn’t specifically stated to be American.

[naturalman1975]