I should have known. The pink is mentioned in the Moth Bible, but as so often in years gone by, I was not paying attention in class. My lucky break came late yesterday afternoon when I took in the moth trap from the rain and noticed that the Black Arches which had come overnight was still there. The crucial difference from the morning was that something, perhaps the rain, had persuaded it to reveal a little of its underwings, like a nightie. When I shifted the box, it slid them open a little more and the pink blazed out.
Can pink blaze? Well it did for me. It was such an unexpected contrast to the white-and-black forewings and the grey below. I coaxed the poor insect to open its wings wider until it lost patience and flew off. But it was sleepy and made progress like a student with a hangover. I tracked it down and persuaded it on to a holly leaf.
This allowed me to take the top picture, showing the pink abdomen from below. A lovely moth indeed. I hereby promote it back to equal ranking with the Marbleds.