Firstly I'd just like to say I really appreciate the work that's gone into Solus and Budgie. Keep up the great work.
This thread is showing that unless an application is currently being used (active and in the foreground) you can't tell if it is just a pinned launcher (closed) or an open application.
It's important to know what applications are open, sometimes you'll need to know something is continuing to process, copy, download (etc.) and hasn't stopped of some reason. And it just generally makes for a better, more efficient experience.
For example in this screenshot Firefox and the task manager are open but the, terminal, text editor and file manager are closed (and just pinned launchers), yet they all look the same.
A small marker to show what is open and what is simply a pinned launcher would be great, this is generally what is done in by other DE's and would be much appreciated.