My opinion which is of course utterly worthless, Is that the dividing line is 5 PM, I get this from US Army manuals/regulations (which are hilariously wrong some times) After 5 PM you do not wear a hat for formal dress uniforms. I assume therefore that during the day one does wear a hat.

Therefore IMVHO during the day one wears a hat and brown accessories, after 5 PM no hat and black accessories.

As for the shoes I match the accessories, obviously Prince Charles does not but I have seen the kilt police jack him up for not wearing the kilt correctly.

The reason for the black shoes at all times may just be that most people in Scotland may not have owned a second pair of shoes and the tradition comes from that.

What you want is to look good. The more formal the gathering the closer I watch tradition and there is a scale of formality and day wear is pretty far down scale meaning good looks trump tradition.