Matthew,
Trying to educate myself with gulls is hard and I cannot help sorry, I bought a good book though (Olsen & Larrson) but its quite pricy!
Gull rings can be reported via BTO / EURING
http://blx1.bto.org/euring/lang/pages/colourform.jsp?coord=pete.rock@blueyonder.co.uk.
Have a look at one I found last year here:
http://jhbirding.blogspot.com/2009/02/kirkby-gravel-pit-gulls-5-february-2009.htmlhttp://jhbirding.blogspot.com/2009/02/coningsby-lincolnshire12-february-2009.htmlThe detail you get back is quite interesting! I believe this might be a ring coding colour of a FERA ring from a landfill tip.
"(Orange (tall) ring with green / black code (4 numbers) on tarsus and BTO metal ring on other leg.
c/o Phil Bone, Food and Environment Research Agency (FERA), , Sand Hutton, York YO41 1LZ, United Kingdom.
e-mail : fera.gulls@gmail.com
note 1 : used numbers are from 0001 till 9999. "Hope it helps a bit?