http://timetothinklanguages.blogspot.co.uk/2014/03/ooh-very-excited.html#more and was desperate to implement it in my department. We started off with 'green' being good, but that clashed with our school's 'green pen policy', where the pupils use a green pen for self review before handing their work in. So I just replaced it with yellow and voila!
It's supposed to make the pupils think more about their mistakes and also make marking a little easier (I have made comments too on the next page of the book!). I'm handing the work back tomorrow, so we'll see what they think!