At the old fortress – familiar to anyone who watched Daenerys Targaryen liberate the Unsullied at Astapor – cannons gaze out to sea, facing down non-existent foes. There’s broken indigo and cerulean everywhere – on arches, tiles and window shutters – and especially at the harbour, almost solid with boats, many home to feral cats. Just off the coast, where the fishermen get their catch, lies Mogador, known as the ‘Purple Island’. The Phoenicians were drawn to Mogador 3,000 years ago for the unique pigmented mucus in the island’s spiky murex shells, from which they manufactured dye.