http://gull-research.org/glaucoides/pdf/primpatterns.html. So, there is no point in repeating information here. All I have done in this post is to pull out some examples of a few extreme adult birds seen on the trip.
A pale bird, both in terms of grey tones and the apparent absence of any dark pigmentation in the primaries. (Tempting to think about birds with paler upperparts as glaucoides, but see final images in this post).
Dark on the outer web of 3 primaries (b or c in Howell and Mactavish)
More dark still (closest to k).