I designed the 12-bit rainbow palette for use on https://grid.iamkate.com. It consists of twelve colours chosen with consideration for how we perceive luminance, chroma, and hue. The palette uses a 12-bit colour depth, so each colour requires only four characters when specified as a hexadecimal colour code in a CSS or SVG file. For more details, see https://iamkate.com/data/12-bit-rainbow/