i have the same vitz your talking about and my rear windows are black as well..
The police did stop me a few times saying you have tinted your windows, so i always lower down my rear window and tell them its not tinted, One time an officer literally checked with his nails whether there is a tint paper installed or not, and then he said ok you can go..
So nothing happens just tell them its not tinted and if this is such an issue then they should stop importing these 'illegal' tinted cars.