I was looking at the photo and thought to myself how lovely Camilla looked. The pinafore effect is, IMHO, pretty well non-existent. The ensemble is fitted perfectly, and the choice of blouse works extremely well with the almost severe cut and colour of the body of the dress which is softened by the delicate print of the georgette type material of the blouse with its delicate black, white and grey pattern, offset by softly feminine sleeves whose cuffs seem o fit Camilla's style perfectly.
The wrist bands look to be able to be pushed up to that three-quarter length that she often seems to favour, especially in summer. She seems to be tailoring her style to fit her engagements and I would suggest that wearing a gorgeous brooch would seem frivolous to the occasion in such a close setting. That is not to say that if she stepped out latter with one of her natty little capelets there couldn't be a discreet little bauble or a whacking great eyeful of gorgeous glittering glory. But not for occasions such as this.
On a more personal note, I have to admit I love her wholehearted adoption of suede (and wool lined) knee high boots. She is both practical and elegant in them and even in the Palace I imagine there are significant drafts around the ankles. (Heating that great place must cost a pretty penny),