Glass Tint

What has been your experience? Am working on a '68 cuda but this probably applies to other Mopars. I seem to be seeing different glass "tints". I believe the factory had a "clear" and an optional "tinted". There is quite a difference between the two and easily seen. When I look at my glass, which I assume is the "clear", there is to me a light green tint. Am I really looking at a clear glass? Does age cause this? Or does the factory "clear" really have a light tint? I am just confused because some are selling "clear" glass as tinted.