I've been thinking about these so-called "rules" from the royal family. Apparently there were loads of people bleating that Meghan broke protocol by wearing dark nail polish....
... and my new theory is that the queen sits around bemused whenever someone is brave enough to tell her that the media/public are outraged because Meghan is wearing dark nailpolish/ a different neckline or whatever. They're not RULES. They're a set of social niceties that have largely been accepted but that can and are changed. In the same way that even in the 15 years I've worked in the City I've seen a HUGE shift in what is acceptable for both men and women to wear. When I started, no woman ever wore anything except a suit. Even a dress was usually part of a suit set. Very very occassionally, a very stylish woman might wear a very simple shift dress of some sort with a slightly different jacket, but it was rare. Similarly, the men all wore suits and ties. Every day (except casual friday). Now, in the city women in full-blown suits are much more rare, with co-ordinating separates more common and lots of men don't bother with suits, even for meetings.
I believe it's the same with the royal family. It's just that because the queen is still around, they're not moving as fast. My great aunt is pretty modern and forward thinking, but I find myself instinctively dressing a little smarter when having lunch with her, even if it's just in the local pub. Even though I don't think she'd have a single moment of concern if I was wearing jeans and a jumper (like everyone else).