Identify what is already there
Some vehicles come with darker rear glazing from the factory. It can give a different appearance from the clear front glass. Ask the installer to identify existing film versus factory-colored glass.
Match the goal, not just the color
If you want front and rear windows to look similar, consider how the view changes with interior color and lighting. The final choice should still meet visibility and local requirements.
Review added film separately
A darker appearance does not by itself tell you the solar-control performance. Review the actual glass and any proposed film specification.
Use a measured plan
Treat each pane as part of a system. A careful consultation records existing glazing, proposed film, and the intended finished appearance.
General template education. Product claims, local requirements, and studio policies should be checked against the actual vehicle, product, and business before a real launch.