Finally, I just started with the swans because I could just see what colors they needed. Usually in oil paintings, you start with the background first so that the foreground looks like it is over the background, but I did it backwards.
The funny thing is that once I had the swans finished, I could tell what colors I needed to mix for the water. It was a funny, muddy color, but with the right highlights and shadows I think it worked really well and I am very happy with this painting. I think it would make a lovely greeting card. I am renaming it "Duet".