Looking back at this photo from years ago, I noticed I had captured (out of focus) a rare Blue Morph of the Ross's Goose.
The Blue Morph in Snow/Ross's Geese is believed to be controlled by a Mendilian dominant allele making the geese dark with a white head (instead of solid white). Blue Morph Snow Geese can be reasonably common in some populations representing 10-30% of the geese.
But Blue Morph Ross's Geese are much less common. Some studies estimate the frequency of this gene in pure (non-hybrid) Ross's Geese at around 1 in 10,000 Ross's Geese!