>>2147044How tight is your control over pollenation? Are there only two individuals within the range of your pollenators?
I live in a city, and wouldn't count on any method short of a full on greenhouse to isolate mine from the local populations. Even harvesting down to the two most desirable specimens. Even deliberately manipulating conditions to induce seeding. Some idiot, somewhere, has cabbage bolting at the same time.
Also, if you're breeding for coloration you may want to look into whether there's more than one sequence (are they called alleles?) affecting it.