It was about 20 years ago when we planted several purple Michaelmus daisies in our garden. Over the last few years there has been a mysterious and very welcome transformation happening. They are changing colour! Some of the originally deep purple blossoms have become a bright rich medium purple. Some plants now have pink flowers.

Anyone know why these plants would change colour? I am thrilled with the developments, but can't hold back my curiosity about what would cause this transformation.