Here's what the new indicator looks like in the default "DreamHost's Simple Theme" . The color and shape are different, but it is subtle:
If you select the "Default Theme", the new indicator is a bit easier to see because tags are grey:
Another way to see new topics is via notifications (in
/u/user/notifications or the user popup menu on any page). New topics you haven't visited appear with a light blue background and thus are easy to spot:
To get these notifications, I think you first have to setup Category or Tag watches in preferences (
Personally, I just use RSS or new-topic email-notifications on Discourse forums, so I don't have to visit the site regularly to stay informed.