Whilst watching this Green-winged Teal at Virkie yesterday (forgive the poor photo) I was struck by its contrastingly pale loral area. I haven’t noticed this before, and don’t recall seeing it discussed (though Reeber does refer to a pale comma at the base of the bill in his discussion of head patterns).
I initially wondered whether it might be a hybrid feature, but after looking at numerous images it seems to be a regular feature of some male Green-winged Teals but not of Eurasian Teal. It therefore seems to be a supporting feature when present. Informed comments will be welcome.