I've already noticed in some old Japanese Geisha representations that they appeared with the darkened teeth. Never thought it was on purpose, and even desired and a sign of commitment and adulthood. It is so interesting to know and to research all about one tradition. As you said, it is all about the context. The beaty signs, most of them remain the same. The cultures are the ones that change, and he way that certain cultures nowadays can "spread" more their set of believes and traditions, they became much more common worldwide.

a Japanese person 200 years ago might have been just as horrified by Botox lips or giant fake breasts as we are by black teeth.

I can say that luckily that other "signs" for the outside that women aren't "available" were adopted 😅