May I use the front panels tones?

Halli hello, my question to you is: I have seen a scale last time, which had the front car discs Very dark tinted, almost darker than the rear windows. Can one now already driver and passenger windows so dark tones that one can no longer look in? Or is that not a foil at all? Are the windows from the factory already so dark? Where can one buy these windows? Thank you, Dani