Lawn / Grass has turned black !! (dark brown)

Any ideas what this is and how to get it back to green? Anything that can be used that's natural/organic (organic gardening style) if not anything will do

 

Difficult to tell from the photos but as there are patches of living grass amongst it I'd say it looks like a large patch of moss which has been killed off by iron. Have you attempted a moss kill recently/had a large iron bath on the grass fro a while and just moved it?

 

Yes a little bit of living grass but a lot of dead moss as you say but nothing has been placed on the grass at all. Not tried anything yet, as only just gone this colour after looking quite healthy before!