It was the King Color, of which all the lesser colors are merely partial and wishy-washy reflections. It was octarine, the color of magic. It was alive and glowing and vibrant and it was the undisputed pigment of the imagination, because wherever it appeared it was a sign that mere matter was a servant of the powers of the magical mind. It was enchantment itself.

But Rincewind always thought it looked a sort of greenish purple.

From: Terry Pratchett, "The Color of Magic"