This didn't photograph well; the flower spike was tall enough that it was higher than the display's background, so I caught a lot of greenhouse roof in the photos and it got kind of washed out. Which is too bad, because I was very impressed with it. Not only is the color neat, but I don't think I've seen this kind of patterning before.
Unfortunately, I have no idea what its name is, so that's all I can tell you about it.
In unrelated news, letting the dill go to seed in 2015 did finally get me some swallowtail caterpillars. I've been trying for at least a few years, and this is the first year I've spotted any.
I think, based on what I've seen flying around this year and what I've seen on-line, that this is probably a black swallowtail (Papilio polyxenes). The caterpillars were only visible briefly; I don't know if birds got them or if they're pupas already. Happy to see them either way; it was maaaaaaaaaybe even worth all the dill seedlings I'm going to have to pull up next year.