Note the brown hood, not black as in Mediterranean Gull, a wrongly descriptive bird name if ever there was one. The hood extends from the throat, behind the ear coverts and up onto the crown; it does not encompass the whole head as in Mediterranean Gull. The white eye crescents are narrow and do not meet in front of the eye.
The bill is slender and all dark/deep red and the legs are dark red.
The upper-parts are plain pale grey.
The primaries extend well beyond the tips of the tertials and black with white outer edges and small white tips, becoming increasingly larger on P7 and P6. The outermost edge of P10 is black forming a black leading edge to the white window.
The overall build is slender, rather attenuated and with a small head.
Black-headed Gull - Adult summer, unkown, Essex March 2007
Note the same features as detailed in the previous image.
Another variation on the leucistic Black-headed Gull theme. This birds upper-parts are white, or extreme end of the palest grey, whilst the bare parts and primaries were normal. It was a strikingly white looking bird in flight.