Most cars these days have green-tinted glass all round, but not very heavy.
In Florida, you can tint all your windows so long as they allow at least 20% transmission, and your front windshield down the the AS1 line (look for it… it’s on every windshield).
Should you choose to leave the front two windows untouched, you can tint the rest darker.
Of course, there’s no equipment to test the tint, and no enforcement, cuz nobody gives a damn, so lots of folks my age (college) have 6% tint and nobody says a word about it.
I personally have 22% all the way around, cept the windshield. It cut down ont he heat down here in 90-100-higher degree summer weather, especially when the car is parked. Also, it makes the headlights from cars behind me much less a nuisaince (sp?), and besides that, it looks pretty cool (my car is teal colored, and teal and black go together well)
I imagine the hot weather here is the main reason for the lax laws. As I understand it, tint is illegal all together in New York