We saw a pair of ducks in a drainage ditch (not a great background for photos!). The male immediately flew, but the female stuck around for a few pictures.
She flashed a bit of blue as she was walking around, leading me to think she might be a blue-winged teal.
And when she flew, I saw the flash of blue, and I was sure that was what she was. However, once I got home and checked out the bird book, I began to have doubts. One is that her bill is dark, and she doesn't have a "white crescent" at the base of the bill. Also her legs are orange -- not yellow. The pictures suggest that she may be an American Black Duck. This duck has blue along the trailing edge of the wings, orange feet and white/gray on the inside of the wings. The only "gotcha" is the "dark olive bill" -- this duck's bill seems a bit darker than that.
Here's a bit of an artistic shot of the wings.