Doctor/River
I know how a perception filter works, thank you very much. I was looking for an explanation for the change. It is my understanding that the affair with the costumes was attributed to some kind of magical enchantments. I suppose there could be something similar at work here. But considering the portal's effect on the TARDIS' temporal geometer, it is possible that it could have affected the perception filter in some way and cast it town-wide.
If you change, I'm going to be very angry with this town.