New notifications in the notification menu show blue until visited, but the behaviour is erratic and sometimes they will only clear if the menu link itself is followed, not if the topic has been visited by another rouite. This occurs both here and on our own site, but the behaviour is inconsistent/intermittent and I can’t find a reliable way to reproduce it.
This is an issue because the notification menu is not easy to use by keyboard. The shortcut which opens it does not give focus, so links can only be accessed by tabbing through from the top each time. I generally use j/k navigation to move through new/updated topics and just check the dropdown periodically to ensure I haven’t missed anything. The fact that sometimes the blue highlighting clears and sometimes it doesn’t just makes this confusing and unreliable.