Mine are purple. They bloomed about a month ago, and I expect them to stay purple through most of the summer. I'm in 7A and the surface of the pond often freezes over the winter, but my pond is 3' deep so it doesn't freeze far below the surface.
Piggybacking on the OP's question, how deep do you place the basket? I originally built my pond with ledges so that I had a 1' deep ledge and a 2' deep ledge (then the floor is at 3'), and the nursery I bought them from said to put them on the 1' deep ledge. But they grow up WAY above the surface! I worry that if I put them too deep, though, then they won't do as well or won't come back next year.