While the main body of a Hollerith card was invariably a light tan, it was typical to have a quarter-inch strip of color across the top. The idea was that you

While the main body of a Hollerith card was invariably a light tan, it was typical to have a quarter-inch strip of color across the top. The idea was that you could tell the payroll program (purple) from the inventory program (green). It was also helpful to see which cards in the deck had been revised, if any, as they’d be a different color. Kind of like “revision pages” in a script, or output from “diff”.