New from J.K. Rowling
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.
The four Hogwarts houses have a loose association with the four elements, and their colours were chosen accordingly. Gryffindor (red and gold) is connected to fire; Slytherin (green and silver) to water; Hufflepuff (yellow and black, representing wheat and soil) to earth; and Ravenclaw (blue and bronze; sky and eagle feathers) to air.
Colours like peach and salmon pink are distinctly un-magical, and therefore much favoured by the likes of Aunt Petunia. On the other hand, shocking pink, as sported by the likes of Nymphadora Tonks, conveys a certain punky 'yes, I've got a Muggle-born father and I'm not ashamed of it' attitude.
Colours also played their part in the naming of Hagrid and Dumbledore, whose first names are Rubeus (red) and Albus (white) respectively. The choice was a nod to alchemy, which is so important in the first Harry Potter book, where 'the red' and 'the white' are essential mystical components of the process. The symbolism of the colours in this context has mystic meaning, representing different stages of the alchemic process (which many people associate with a spiritual transformation). Where my two characters were concerned, I named them for the alchemical colours to convey their opposing but complementary natures: red meaning passion (or emotion); white for asceticism; Hagrid being the earthy, warm and physical man, lord of the forest; Dumbledore the spiritual theoretician, brilliant, idealised and somewhat detached. Each is a necessary counterpoint to the other as Harry seeks father figures in his new world.