Actually Texas law states that the windows immediately to left and right of the driver cannot be less than 25%. The left/right windows to the rear of the driver(4dr car) can be whatever you want. They are exempt in the code. The rear window can be as dark as you want if and only if you have functional side mirrors that allow you to see at least 200 feet back from the car.
Hatch Nation #9
"2 by 2 Hands of Blue."