Male Green-wined Teal in flight showing the beautiful green on his wing. Other ducks, such as Blue-winged Teal and Cinnamon Teal, etc., also have green on their wings, so you need to use other clues as well to ID this duck. Photographed at Harris Neck National Wildlife Refuge, GA.
And he has green on his head also, especially noticeably when the sun shines on it. Here you can't see the green on his folded wing.