It's always handy to be able to distinguish good plant material from weed. I've been quite lax at weeding this year and have never quite gotten to the side area up the hill. This little "volunteer" arrived at the very edge of the path, firmly embedded in the gravel. I've placed the Cheshire guard there to ensure that this very old, unusual colour, single variety remains untrodden until all buds have opened.
It is still anyone's guess as to how this little dancer arrived in my garden.