Am I using the wrong setting somewhere? When I read a post, it used to change color to show I had read it and I knew

[usonian]

5. I remember a browser setting somewhere, sometime, that let you change the color of links that you opened.

Since it relies on your browser history to tell the browser what you already saw, it could be that you are in some private mode that wipes or “forgets” browser history ( Not that you are a criminal, but browser history has led to arrests, for browsing sites related to a crime, as in “how to make a pipe bomb” and things like that. )

A few people on DU have inadvertently gone into private mode (easy to do accidentally on a phone)

Best guess without doing a bunch of research.

I also seem to remember one browser that let you “highlight visited links”, or not.

Since it is a browser matter, it will vary from one to another.