Pied Wagtail

My phone really does not take good photos of birds unless they are sitting on my nose. So, sadly a deceased one makes a much better subject. 
A friend found this Pied Wagtail, apparently in perfect condition, lying in the bottom of the Pioneer rescue boat. Over the year flocks of PW's fequent the foreshore and pontoon so it is not unusual to find one dead, but this one had us wondering because instead of the usual black and white head feathers this had marked yellow flushing. Was it a hybrid with a grey or yellow wagtail or perhaps a blow-in from Scandinavia or the Continent? 
I looked it up and found that in the Autumn moult many PW's display a yellow flush initially. As the soft feather tips abraid it fades to the more recognisable pied colouration. So, this pretty thing died in its best bib and tucker.