That would be an interesting test, and maybe something we can do after Shely goes through all the breeds that have (or allegedly have) breed-only variants. There are flowers that I have a bunch of, where I have only one each of certain colors. So I, too, would like to know if those colors are rare, or if it was random which colors I happened to get.
I would also like to know which of the HoV flowers is breed-only. Exterminans said that one variant is, but I've checked various gardens, and it seems to me that I've seen parentless of every variety, in one person's garden or another. Some of them might be seeds they got from the postal pixie, but I have no way of knowing. Unfortunately, that's one type we can't test until next Valentine's Day, and even reporting what we currently have won't work, because people won't necessarily remember which ones came from the post pixie.