A quick search reveals this chestnut staining has been recorded by twitchers at least as far back as 1933. It's probably due to the muddy water the cormorants swim in to catch food.
To be fair most of the Little Pied Cormormants that I see, round the traps, are stained or dirty looking like this one.
Following are some details showing the face close up, as clear as I can get for now. And there is also a picture showing the wings in the sunlight.