Track a post for new comments

Not sure if this was an uncommon feature, but I used [Joey for Reddit](https://www.reddit.com/r/JoeyForReddit/) as my 3rd party Reddit app and one feature I loved in it was the ability to track a post so that you got a notification when there were new comments on the post. This was distinct from the ability to save a post for later and I found myself using them for different purposes:
* Saving posts I reserved for posts I'd want to go back and view days or even months later
* Tracking comments was for posts I didn't care about long term, but wanted to see more activity on before hiding them completely (e.g. a very new post with no comments yet - there are posts that I want to see other people's input on, but don't really care about holding onto long term)

Even just this base functionality would be nice, but Joey had a separate feature (I think?) that was incorporated with it that would show you which comments were actually new to a given post (since you last viewed it) via a different shaded background - this would happen whether or not you marked a post as tracking for new comments, but was especially helpful when revisiting a thread to see what new comments had been added.

Let me know if more detail on either of these features would be helpful, I can see if I can scrounge up examples from Joey if it's not clear what I'm asking for!