Well, I collected some seeds from that plant last fall. They produced several seedlings, only one of which I managed to plant in my garden (or so I thought).
The result was this:
Blue and pink Asters. In person, the flowers on the right are a deeper shade of pink without the hint of purple seen in the photograph.
As far as I can tell, this is only one plant with two different colored flowers, though it is remotely possible that there were actually two seedlings that came up too close together to notice (or separate) when I was planting them. While I would find the former really cool, (and really surprising) if there are indeed two plants here, the all seeds still all came from the one blue-flowered original. Asters are much beloved by bees and butterflies, so I'm sure that open-pollination contributed some genetic diversity to my plants.
At any rate, I'm going to collect seeds again this year, from the original plant, and from the both the blue and pink flowers here, and see what happens.