A big question!
Have seen this discussed on-line several times, but I've never seen any noticeable colour change in any of the irises I've planted and maintained over years.
I'd wonder whether all of the variety of irises were purchased as named plants/cultivars and, especially whether they were each in flower at the time of purchase (e.g. correctly labelled); also, whether there were already iris rhizomes in the flower bed in which they were planted. Related are the facts that some irises are much more vigorous growers than others and that any bee-pollination of iris producing seeds which drop into the clump will not produce identical offspring.
Be interest to hear if others have had real or apparent colour change experiences with irises.
This seems a good reference:
http://www.wildflower.org/expe...
