The world is awash with the color purple — lavender flowers, amethyst gemstones, plums, eggplants and purple emperor butterflies. But if you look closely at the visible-light portion of the electromagnetic spectrum, you'll notice that purple (which is different from bluish hues of violet and indigo) is absent.
That's because purple may be made up by our brains; It exists only because of how the brain processes color.
