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”.

There was indeed often a colored stripe at the top of the card. At computer centers I used, this stripe was used to indicate what JCL (job control language) statement was on the card. So the computer center would have a big stack of pink cards already punched with the statement to invoke the FORTRAN compiler, for example. The teacher told you to put a pink card at the front of your FORTRAN deck before you submitted it, or it wouldn't work.