Finnish Herring Gull become leucistic

This amazing bird, white CE499, was ringed as a normal-coloured pullus L.a.argentatus at Rääkkylä near Joensuu, E-Finland 25.6.2000 by a gull-enthusiast Risto Juvaste. It has a long colour-ring history with over 150 controls 2000-2009 mostly from Joensuu rubbish tip, period 25.3.-16.10. It has also been controlled at Tampere, Anjalankoski and Savonlinna. It was controlled as a normal adult Herring 2004-2006, at least there was nothing unusual with the control situations. At the age of seven, 8th calendar year, it was surprisingly partly leucistic. Now, at the age of nine it is almost complete white! The dark pigment seems to reduce with age. Two outermost primaries still have a faint dark pattern, but how long? This individual clearly shows how careful one must be when progressing an identification of a vagrant or abnormal gull.
Pictures here:
http://www.tarsiger.com/gallery/index.php?pic_id=sampsa1256556981&lang=fin