Images of 4th-calendar year Lesser Black-backed Gull Larus fuscus graellsii (Dutch intergrade) Green K.AMU, seen in the gull colony on the isle of Texel, the Netherlands, 3 May 2014.
It was ringed as a pullus in July 2011 in the same colony.
In rest it shows an overall adult appearance apart from the brown hue on the outer lesser coverts and the outer greater coverts, the lack of white tips on the outer primaries and the presence of black on the bill.
In flight its age is much more obvious with much black that can be seen on the greater primary coverts and the outer secondaries on the upper wing, the under wing showing brown fringes in the lesser coverts and primary coverts, and the presence of black spots in the tail.
Also note the tiny mirror on P10.
I first encountered Green K.AMU in September 2013 in Katwijk aan Zee, the Netherlands. At the time it was still very much moulting its feathers. Also note the colour of the bill and legs: