s an ambitious young scientist at Cambridge University, Isaac Newton famously trained a glass prism on a narrow beam of sunlight to divvy the white light into its constituents, a dazzling rainbow of colors. There were no demarcations between one component color and the next, no clear way to count just how many basic hues were on view, but Newton was a systematizer with an appreciation for the number seven. After all, seven was synonymous with luck, and it showed up everywhere in Western culture: there were seven days in a week, seven notes in the musical scale, seven wonders of the world, seven virtues, and seven vices. Why not seven colors in the rainbow? And so, Newton specified as the primary ingredients of white light the septet captured by the old childhood mnemonic ROY G BIV: red, orange, yellow, green, blue, indigo, and violet. Some insist that die list should lose the penultimate letter. “It has never seemed
