It seems to be the norm when it comes to un-openable rear side windows as far as the place that did my last 3 cars. I see the same on other cars too. Yes, they do look a bit darker, but it doesn't look bad. In fact, you'd normally just think that the difference in appearance is because the rear interior is darker than the front, and you're not really to see right through to the other rear window to the same degree as looking through the cockpit windows. The added tinting on the rear sides and the rear window also help keep prying eyes out.

Additionally, here in South Florida, it can get pretty hot. You really need as much tint as the law allows, and where the law allows, to keep the interior as cool as possible. I'm at the legal limits all the way around.