Blank Punched Cards
Plain rectangular cards were available printed on just about every color of card stock. Square corners tended to fray faster than cards with round corners, particularly if the cards were mixed with cards that had rounded corners. Nonetheless, the cream colored card here was probably used routinely for programs or data.
Because the uncut-corners stood out from round-corner cards, square-cornered cards made excellent dividers between unrelated card decks stored in the same card tray. Colors that constrasted strongly with whatever color was used for the decks being divided helped when using such cards as dividers.
Some card users may have saved a few pennies per thousand cards by ordering unprinted cards for routine use, but printing cost so little that this was uncommon. Brightly colored cards with cut corners were, however, useful as dividers between sections in card decks. Recall that, when editing a card deck, searching for a particular line of code in the deck involved riffling through the cards by hand. Putting colored comment cards between significant sections of a deck or using colored cards for the headers on significant blocks of code could greatly speed up editing when programs grew large.
Note that these cards are shown with the cut corner on the left, but the physical card, being made of colored cardstock, could as easily be flipped over so the cut corner was on the right. When used within a deck of cards, these cards would typically be flipped so that the cut corner matches the other cards in the deck in order to minimize fraying on protruding corners. When used as dividers between decks stored in a card file, they would typically be flipped so that a round corner protrudes on the side that is cut in the filed cards, so that the divider card stands out from the decks it divides.