where do you want to change the tag color? I mean which page?
in all pages. On header in envinet.ning.com you can see a black text: "idee per la sostenibilità". I'd like change that text in green
Change to suit. put it in advanced css
Can I put that piece of code at the end of css "file" (I'm not a css wizard!) ?
Yes you can put that code at the end of CSS box.