I know this is probably way off topic but I have been wondering who to ask for a while...
I have noticed the "diplomatic class" of the Vatican wearing an idiosyncratic form of white tie, as at:
Can anyone advise what the origin of this form is? It appears to be the usual white tie, but without white marcella waistcoat and instead a black one. I understand that was an older form of the outfit, and therefore I assume this usage has simply continued in Italy / the Vatican?