Debug Mode Using Element Fill Feature

I believe that happens because when you close debug mode, any area that duplicants haven't actually explored goes black. It is weird that it's just that rectangle rather than the entire outside area.

There are now two extra options on the paint tool (you need to scroll down to see them completely so people might accidentally miss them) :

- Allow FOG reveal

- Prevent FOG reveal

... or something along those lines. Make sure you toggle "allow" on and "prevent" off otherwise you get those square black boxes and they will never go away, even if you move a dupe through it.