Sometimes I open several instances of one program at the same time and have to switch between them every few seconds and get totally confused as to which is which (they all display similar information, except few bits).

I'd like to have each one of them color-coded, different shades, window border, etc or have anything visual to make them differ from one another to ease the confusion. Ideally this would happen automatically when I launch a new instance.

I guess this belongs to the window manager so mine is xfce.

In one of the window managers I used to use a huge label was displayed each time I switched between workspaces, something like that (with window title or simple number) would do as well.

Any clues?