I'm planning to visit Stuttgart. I wasn't in Germany for a year and I'm puzzled by unclear information about the current state of Umweltplakette. The site https://www.blaue-plakette.de/ writes as they were there, but my collegues having relatives in DE has not heard about them, and the site looks a bit strange (it's made as it was official, but it looks it's operated by some private entity).
Is there a Blaue Plakette, or the green one that I currently have should be enough for fine-free visit?