I couldn't find anything about this. If it has been done before, please direct me.
Would it be possible to change the color of the name when the user is online? So for example, if a user is offline the name would be black; would he/she be online the name would be green. And it should be displayed this way in all places where the name is shown. So both in the message list AND on the profile page.
If this won't be implemented in the near future, perhaps someone could create it as an add-on?