What kind of car? If it's a Q, I don't believe that they came tinted from the factory! Aftermarket film on a car for as little at 6 months will fade or lighten to a point where you can't match it exactly. They call it color fasting......
If you are trying to match factory tint however, the glass has the shading embedded in it so it dosn't look like "Film". It has a deep almost black look to it. Most applied films wont match because they use a different technology to get there shading.
My suggestion would be to look for a Lumar Formula One store and ask for Pinnacle. It is a new Ceramic film that will be the closest match to OEM.It also has superior optics and a bunch of other advantages. The most important being that it can't turn purple over time and it wont look shiny in the sun. Two things the OEM glass will never do.
Here a linkhttp://
www.formulaone.com/
CheersScott