According to many metaphysical practitioners and believers, aura colors are caused by vibrations. Every atom and molecule in the universe translates itself into patterns. The patterns emanate from the body as vibrations, and the human eye can be trained to perceive these vibrations as colors. Just as we cannot hear sound waves with the human ear, aura colors are visible only to a minority of people. But the human eye is gradually gaining the power to see aura colors, according to Gerald Heard, in his classic 1939 book Pain, Sex and Time. The aura color wheel consists of seven main colors: red, orange, yellow, green, blue, indigo and violet.