Many bigger german towns are requesting a LEZ sticker and in nearly all of them it must be a green one. My car will get only a yellow sticker, it´s 10 years old.
I think that i do not need a sticker in my "homeland", neither red, yellow or green. The sticker is only applicable for the inner center of the respective town, in many cases the old town district. In case i want to visit those areas, i will park the van outside the green zone and take the bus or the bicycle. And the parking situation outside the centers often will be much better than in the inner center. It's just a matter of planning.
Generally all highways, motorways and 99% of all roads are sticker-free, so what. And in case i might drive into a sticker area by chance, i will turn the car and go back, nobody will chase you....the neighbouring town might be looking the same, may be they will not request a sticker there and so i know where to spend my money

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And nearly all "Stellplätze" are outside the green zones, so no stress.
Since years i am driving without sticker and it never was a problem, as i said, i little bit of planning.
The only sticker i have on the car is the wildcamper sticker



So i think "no LEZ sticker" is not a show stopper.
Bernd