(2 images) Herring Gull H - 117045 2cy (argenteus), January 04 2002, Boulogne/Mer, France (50.43N-01.37E).

Ringed in Belgium as pullus in summer 2001, with metal ring Bruxelles H-117045, ringed as pullus on July 04 2001 at Zeebrugge (51.20N 03.11E). This bird was rediscovered in June 2002, at the same spot. Compare moult pace in these photo's and especially the state of the greater coverts. Boulogne/Mer in NW France has a strong marine influence, with western (salty) winds; see the map in the distribution section. An individual with most scapulars moulted for second generation feathers. The last moulted lower scapulars show a buffish tone on the centres. The upper scapulars, which were moulted earlier, last autumn, are bleached by now and the buffish tones have turned white. In the lowest row of scapulars, the feathers are still juvenile and abraded.
The partial autumn moult in argenteus (moult from juvenile plumage into so-called "first winter" plumage) includes the scapulars, body and head feathers. This moult starts as soon as the nest is abandoned (late June) and continues until January. In general, the head is paler on throat and forehead. The second generation feathers on the breast are paler as well. The feathers on the vent and the under-tail coverts are still juvenile in most 2cy argenteus by January. From last July onwards, the mantle and upper scapulars were moulted to second generation feathers, showing an anchor pattern and a dark base. The lowest row of scapulars are still juvenile or actively moulted by March in most 2cy birds (contra e.g. michahellis). The notched pattern of the juvenile tertials, lesser, lower lesser and median coverts is not very obvious anymore, as the white parts are largely worn away. The juvenile greater coverts show a 'piano-key' pattern in argenteus; on the outer greater coverts as well. 
The secondaries, primaries and primary coverts are dark with a small white tip, but the juvenile inner primaries show an obvious pale window, prominent from below and above. The under-wing is rather uniform grey-brown patterned. The tail has a broad sub-terminal band and isolated dark bars on the basal half. The iris is dark, the bill is blackish, sometimes with a paler base, and the legs are flesh-pink.
Note that the bird in the background of the top image is a 3cy argentatus from Scandinavia, and not a 2cy argenteus.

photo above: H - 117045 2cy, January 04 2002, Boulogne/Mer, France (50.43N-01.37E).

photo below: H - 117045, 2cy, June 13 2002, Boulogne/Mer, France (50.43N-01.37E).

Argenteus has a partial moult of head and body in spring. It starts in January and ends by May, leaving birds in so-called "first summer" plumage. The head and under-parts resemble the pattern in 1cy birds, although the head and breast turn much paler by June. The lower scapulars may still be moulted to second generation feathers in March, the new feathers showing a buffish tone and a neat pale fringe. 
The Belgian-ringed H-117045, was seen again in June 2002, at the same spot. The complete moult has just started with the innermost median covert. The upper tertials has been shed as well. Compare the images from January and June: the tidy plumage is abraded by June. The juvenile greater coverts are reduced to single shafts and the median coverts are very bleached. The former piano key pattern is hardly visible. The tail-feathers and outer primaries have lost the deep brown tone and look paler, bleached, dull brown. Now the greater coverts are largely reduced, the secondaries lying underneath are clearly visible showing the dark brown centres and small pale fringe at the tips.
In the January picture, the lower upper scapulars are visible as white centred second generation feathers with dark anchors. Suddenly, these feathers look pretty fresh in the June picture: the lower upper scapulars have been replaced for third generation feathers which nevertheless are very much the same to second generation feathers regarding their pattern.