Black tie, Prince Charlie, but the tie is DECIDEDLY not black

[Janner52]

Continuing on the subject of the tie colour, l have to say that my take is that if the ticket or invitation states “Black tie” it means exactly that and anything else could be construed as disrespectful to the host’s wishes. I do understand that, in this day and age less specific dress codes can be suggested and in that case freedom of expression is acceptable.
Fortunately with the kilt, as can clearly be seen in the then prince’s attire, there is scope for personal style and he certainly has form for displaying that.