I am trying to black list a program from appearing in the application indicator and wondering how I can achieve this. To give my question some context, Steam appears in my top panel now and I wish to block it from appearing there or modify the icon.
This is not so much an answer to the question, but instead a method of removing Steam from the system tray. For the radiance theme that it appears you are using, open a terminal and run
If ambiance is being used
Once this is done restart steam.
This will only work if there is no steam_tray.png in the folder. If there is move the file before issuing the command.