I kind of work on a rule that a light coloured frame should have black components and a dark coloured frame should have silver components.
And there shouldn't be too much mixing of the two.
And definately stem, post and chainset should be the same colour. It's the holy trinity isn't it?
By the above definition I need to find a bright yellow seat post, to match the cranks and stem then on one of my bikes. Can't see that working even if there was someone who made them.
I'd say there's too many exceptions to those rules to set them in stone.
I was going to say don't mix your anno colours, but then was reminded that there are losts of bikes with different anno colours mixed which fit with the overall colour scheme, so even then you can't make that a rule.