[Edi]

On any given turn you could lose upwards of 15 or 20 forests if you can flag them (like e.g. Druid and Witch can), so that idea loses its appeal really fast. The constant messages would become really aggravating in short order.

At max zoom you can see ownership of squares just fine (at least for the brighter or stronger colors like red, yellow, white etc), even though the only recognizable things are the general terrain features and some of the more distinctive structures (e.g. city). However, you won't even need max zoom and if you just zoom out at the beginning of a turn, you should be able to see if any of your holdings have a fat line across them.

The darker colors like blue have a little bit harder at max zoom, but you really don't need it that far out.

Playing on max zoom all the time is practically impossible.