One of the classic rules in fashion is that you don’t wear white after Labor Day. Of course, people can wear whatever they want when they want to, but the rule has actually been around for decades. Here’s one potential origin of this rule:
As Time notes, in the early 20th century, white was worn after the holiday by Americans who lived in cities but who could afford to leave the area for warmer climates in the colder months. They wore white and other bright colors instead of the darker ones typical in the city during the fall and winter.
Labor Day is celebrated on the first Monday of September, which is typically considered the end of summer. So this is when people would swap their bright colors for darker ones. People who came from “old money” began to use the rule and other social quips as a way to differentiate themselves from those who came from “new money.”
By the 1950s, the rule became more solidified in American culture.
But not everyone agrees with this explanation. Columnist Judith Martin told Time, “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.”