Thank you! That's exactly what I was looking for. I don't know how but I completely missed this button...
In the dialog for creating a new session there are blue monitor screens in front of each target. In the past I could change the color of these screens to diferenciate them easier by just looking at the color. After starting a session with one of the targets the color is also used for the icon in the tab and for the file list's background. I still have the different colors from former changes but I cannot find where to change the colors now for new targets. I've found only the option to change it temporarily for a tab, but after closing it it's color is not being saved for the next time.
Has this option disappeard or has it been moved and I am not able to find it?
Thank you in advance!