Since the introduction of the linked tabs & their colors, it is a bit more difficult to quickly determine, which tabs are actually active.
I experimented with different colors, but i think, an option to have a thin extra frame around the active tab would be better.
Have you turned on Preferences / Folder Tabs / Appearance / Draw folder tabs using visual style?
Try turning it off and you'll get some extra shadowing around the selected tab.
Ok, that´s already much better now. Thank you.