Because looking for the expiration date on the bag takes way too long: WiseBread tells us that a commonly used (though not legally binding) system among bread makers allows consumers to figure out the day of the week that a given loaf of bread was baked by glancing at the color of the twist-tie that wraps it. Blue is for Monday, green is for Tuesday, red is for Thursday, white is for Friday, and yellow is for Saturday. (Apparently, by custom, fresh bread was not delivered on Wednesdays and Sundays.) The colors proceed in alphabetical order, B-G-R-W-Y.
Though this scheme gets the “true” verdict from Snopes, use it to guide your bread-purchasing habits at your own peril: Apparently, the bread color code can vary by region and country. Snopes recommends that you “Contact the manufacturer of your favorite brand and ask what (if any) color-coded tag system they adhere to and what their delivery schedule to your favorite store is, then let your selection be guided by that,” though that sounds like it’s taking it a little far.