Although Labor Day is a federal holiday to celebrate employees, the event comes with a tradition tied to the fashion industry. Although in modern times it is not as observed as before, according to history, people shouldn’t wear white the day after Labor Day.

Luckily this is not a law, so nothing will happen to those who wear white; however, the sartorial rule marks the end of the summer and the beginning of autumn.

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In simple words, in summer, we wear white to stay fresh, while thick dark fabrics keep us warm in the cooler months. This tradition began in the early to mid-20th Century. “It [was] insiders trying to keep other people out,” says Valerie Steele, director of the Museum at the Fashion Institute of Technology, in an interview with Time, “and outsiders trying to climb in by proving they know the rules.”

However, according to Marie Claire, Judith Martin isn’t happy with this theory. “There are always people who want to attribute everything in etiquette to snobbery. There were many little rules that people did dream up in order to annoy those from whom they wished to disassociate themselves. But I do not believe this is one of them.”