I used to be really into this anime when I was younger, around 2003 to 2006 I think.
It was about kids with powers saving the environment. I think the main guy had greeny black hair and the girl had pink. My favourite character was this guy who could turn towels into steel, and he had black hair and a burn scar over his left eye, like Zuko and Todoroki.
I suppose you're reffering to "The Law of Ueki" an old anime where the main char can turn trash into trees.
The plot isn't about environment, but there is a character that can turn his towel into steel.
Kousuke Ueki, a student of the Hinokuni Junior High School, is picked by a Celestial King Candidate, Koba-sen, to participate in a competition where people battle out to become the Celestial King and only the strongest will prevail. Embodied with the ability to turn garbage into trees, Kousuke will be joining in the battle against other junior high school students in this selection. This sets the premise for the earth-friendly battle where the students will pit their powers against the rest, with a reward of the Blank Talent giving motive for students to win.
