Hi, I'm originally from Baltimore, MD which has a long history of Painted Screens for privacy.
The screens are painted on the outside, and during daylight the paintwork is illuminated - you cannot see thru, into the home, because it is darker inside than outside.
At night, however, interior lighting makes the paintwork 'disappear' from the outside, and outsiders can see in. Those inside may see the paintwork on the screen, and may not be able to see out well, depending on the paint.
I bet if you Google painted screens (or the like) you'll find info, such as the specific paints used, and photos of the effect.