Do you know the name of the cultivar ? Some are noted for doing this. It can be caused by a virus ( the same one that makes those "splotchy" tulips), or ,I think it can also be a "random", or "wild" gene, in the particular cultivar. Another possibility, I suppose, is that the iris is "throwing a sport" (a sport is an abnormal vegative increase, either in color, or "texture" from the original). There is a whole group of these "broken color" iris out there, and some find them neat to grow! Is it just this plant? Or are several different ones involved ". If so, are they in the same bed? If it does it again next season.....I'll trade you for a piece! I kinda' like it! If Lucy chimes in, she no doubt can steer you to some more info on it.....Arlyn
