In my experience these varieties of Asclepias incarnata (swamp milkweed) such as Soulmate and Cinderella do not come true from seed. You may get lovely plants, but the colours probably will not be the same as the parent plant. I just don't want you to be disappointed if you grow these from seed.

I got the plants at our swap last year as little seedlings, and they flowered this year. When they flowered they did look very much like the pictures that I could find of the plant, but I suppose there could be differences.
very pretty anyway and I love it. :)

I gave up trying to keep my selections of swamp milkweed separate. I just grow them all together now and let them seed around by themselves.