Lucas823 is correct. The rainbow is actually formed when raindrops act as a prism and separate white light into it's colors. The spread of the colors is called the spectrum, and the order is always red orange green blue indigo & violet. Red has the longest wavelength so it's light is bent less than violet, which has the shortest wavelength and so gets more. In the primary rainbow, the one usually seen, red is always on the outside, violet on the inside. Sometimes there is a secondary rainbow where the order of the colors is reversed. And yes, black is the absence of light & color.