Aha, I finally located the source of my yellow cosmos (see photo and more information about this plant in the previous post). I can't find the seed packet, but I thought I remembered it being Seeds of Change (www.seedsofchange.com), and sure enough, they are listed in the catalog. The charm of these flowers is that they are the species Cosmos bipinnatus, not Cosmos sulphureus, the one that is usually yellow or orange. This pale yellow is of the species that is usually white, pink, or magenta. I usually have better luck with this species, for some reason, so I was delighted to find a yellow one.
Another surprise. The catalog also lists a variety they call 'Sunrise' with orange/golden and red/orange flowers. They don't give a species, but they say that unless otherwise specified, they are C. bipinnatus. And they sell C. sulphureus separately, so I guess I will have to try this one and see what it looks like!
All of these are suitable for starting in spring through mid summer. The catalog says they can live through a few light frosts, which mine certainly have. An Achilles heel is that the side stems can snap at the point of attachment to the central stem in heavy winds (or when a delivery person tosses a newspaper at them--grrr!).