I hope the Queen will restraint herself and appear as sober as possible (but nevertheless very impressive). I would not mind the Queen wearing this little diadem, eventually with a white small lace mantilla à la Queen Emma, in combination with a crème gown (see picture for the mantilla).
Apparently the King himself will appear less colourful than on a regular joint assembly of the States-General (Prinsjesdag), when he wears a ceremonial uniform. If we have to understand the RVD, the King will wear 'een rokkostuum' which is duller than the usual appearance on Prinsjesdag.