The highlighted track is the result of a search. Click the search button (magnifying glass at the top of the playlist), clear the search term and press apply to remove it.
[edit]Whoops...[/edit]
I did what you said and Whoops... green highlight dissappeared.
By the way I cleaned search terms several times but never pressed apply.
Dotpitch, thank you very much for such fast and useful answer. Now I know what green means
