dq74 said: I divided and transplanted all these from one clump that was always violet purple. The first year, I had a new white variant. This second year, half are white. The violet veining in the white ones exactly matches the tint of the solid violet ones. Meanwhile, an older clump of all-violets have remained the same. The biggest difference I see in location is the white variant appears where grown in day-long full, hot sun.
It's easy to see that these are two very different cultivars, the purple one being a much younger one than the white and purple plicata, which is one of the old dog eared types from much earlier. My guess is one had grown into the area of the other and was barely surviving as it was being smothered by the purple one. Once you divided them the smothered one was able to produce blooms once it had space to grow. It's also possible that pollen from an historic iris was crossed by a bee to the purple one, and you got a seedling that took on the shape of the older model. Either one could have happened, but iris colors don't just change, and they definitely don't change shape.
