Only the focused window matters for "you are here".
There are already plenty of hints:
• Window is maximized
• Title/toolbars not dimmed
• You just opened the window
• Backdrop for modal/transient
• Darker shadow
• In-app cursor / focus indicator
• Window focus notification
See the screenshot, looks pretty obvious to me. I seem to recall the design team working on making it even more obvious for 3rd party apps.