Just look at the twist-tie or plastic tab that keeps the bag closed. Turns out, it's color-coded to reflect the day that the bread is baked. It seems unlikely but Snopes.com dug into it and found that it became an almost-universal practice among commercial bakeries as a way to help grocery store restockers recognize which loaves to replace on their shelves.
To remember which color is which day, put the colors in alphabetical order. Here's the breakdown:
Red: ThursdayWhite: Friday