As noted already, this is an American Herring Gull. Besides the pink legs, note the wide, white tertial and scapular crescents. The latter is not particularly obvious in this photo, but the tertial crescent (created by the broad, white tips to the three tertials creating a white crescent just anterior to the black primary tips). Ring-billed Gull has both crescents thin and nowhere near as obvious. You can read more about scapular and tertial crescents in the In The Scope article in the January 2012 issue of Colorado Birds (
CB_2012_46_1_Jan.pdf), page 78.
Tony Leukering
Denver