Pratchett made up a new colour, octarine, a 'fluorescent greenish-yellow-purple', which is the eighth colour in the "Discworld" spectrum—the colour of magic. Indeed, the number eight itself is regarded in the Discworld as being a magical number; for example, the eighth son of an eighth son will be a wizard, and his eighth son will be a "sourcerer", extremely powerful users of magic with abilities far beyond what most wizards usually achieve (which is one reason why wizards are not allowed to have children).