The Color of Magic

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 like a sort of greenish purple.
--The Color of Magic