I transplanted yellow bearded iris two years ago. Why after two years have they all turned purple? Last year most were a yellow mottled with brown spots.
Believe it or not, this does happen occasionally. A change in temperature, if there were issues during transplant or sometimes even the rhizomes being accidentally dug up can cause this.
Here is an article that can give you more information on why this happens: https://www.gardeningknowhow.com/ornamental/bulbs/iris/why-an-iris-changes-color.htm