The blues and whites do seem to be related, but I get white seedlings from all sorts of crosses. For example, these two came from blue(ish) parents:
10T-03b
11T-20q
But, these came from Twilight of the Gods (an orange iris):
11T-25b
10T-05a
The 11T-25 cross was kind of interesting, it also produced:
11T-25e
11T-25f
Another white seedling came from Magical X Wintry Sky.
11T-14a
This wasn't at all what I was hoping for from this cross, but I'm sure I'll keep it, maybe as much out of stubbornness as anything.
I've crossed Wintry Sky and Magical at least a half dozen times, and gotten just two pods that produced less than ten seeds between them, only one of which germinated. It's kind of a dull color, but it does have really nice form and substance. It's fertile, too, so it may prove useful. Will probably keep 10T-05a, at least for a while, just because it was my daughter's favorite.