My family had long joked about cats' ability to shed contrasting fur on things, for maximum visibility. One day, I saw one strand of fur on a chessboard, straddling two squares. It was dark on the light square and light on the dark square. I pointed it out, exclaiming that the cats had really outdone themselves on that one, producing a two-coloured strand, and aligning it with the border. No, my mom explained, it was probably just a grey hair, and just appeared to contrast with both colours. So I turned it around, and it vanished!