I spent some time visiting family near Olympia, Washington over New Years.  At this location there were plenty of wintering Anna’s Hummingbirds.  Because of feeders, these birds are sometimes over wintering more northerly than they used to.  The males are able to change the colour of their heads by reflecting light in different angles.  An iridescent pink can be created in this particular specie.  Males use these colour changes to signal warnings to other males.  I wasn’t able to get photos of the colour on this specific trip but will add a photo from the previous year in the same location to illustrate.