Witches and wizards often reveal themselves to each other in public by wearing purple or green, often in combination. In Britain (and much of Europe) purple has an association with both royalty and religion. Purple dyes, being costly, were once worn only by those who could afford them; bishops’ rings are traditionally set with amethysts. Green has long had a supernatural connection in the UK. Superstition says that it ought to be worn with care; the fairies are supposedly possessive of it, as it is their proper colour. It ought never to be worn at weddings, due to a further association with misfortune and death. Green is the colour of much ‘Dark’ magic; of the 'Dark Mark’, of the luminescent potion in which Voldemort conceals one of his Horcruxes, of many 'Dark’ spells and curses, and of Slytherin house. The combination of purple and green, therefore, is suggestive of both sides of magic: the noble and the ignoble, the helpful and the destructive.