Izzy gives Prince Charles credit for being, er, ballsy enough to wear kilts in celebration of the union of Scotland and England, but he erred royally in combining a loud tartan with a bold argyle. Either the kilt or socks ought to have been muted or plain.
You see the thing is, he is clearly not wearing an Argyll. I would seriously doubt that he would ever wear an Argyll to a Black Tie affair. He is wearing a doublet and with the level of formality of the event his hose, sporran etc. while perhaps loud are in fact correct, plain or muted socks as he calls them would not be correct, diced hose as worn however are.