TO AUSTRALIANS, it seems like the most absurd, outdated fashion rule in the book. No wearing white clothing after a specific day of the year.

But to many Americans, it’s the age-old adage that no fashionista would be game to rebel against.

So, why aren’t people supposed to wear white after Labor Day?

With the national public holiday fast approaching in the US, I was reminded of this fashion no-no by a fellow colleague who walked into the office this week declaring it was “the absolute last time” she could get away with donning the super cute, white summer frock she had arrived in. And yet, when I questioned why it was “a thing”, no one seemed to be able to explain it, they simply adhered to it.

My heart sunk. Did this mean I’d have to farewell my staple white skinny leg jeans until next season? What about my super comfy white sneakers? My flattering white maxi dress as well? Surely not.

But it seems the origins of this fashion crime are rooted in a very different time, beginning in the early 1900s when clothing was more formal and there were strict guidelines regarding what was appropriate to wear as the seasons changed.

“The post — Labor Day moratorium on white clothing and accessories has long ranked among etiquette hardliners’ most sacred rules,” Time magazine reported in 2009.

Wearing white not only meant that you were on-trend, but also signified that you were wealthy enough to buy garments that made you sweat as little as possible in the scorching summer sun. Basically, wearing white in the heat (think pre-AC days in 38C temps) meant you could afford to ruin it.

But wearing white after Labor day (the unofficial end of summer in the US) at that time might make you the talk of the town — and not in a good way. White was a summer-specific social statement, no exceptions.

Come September, when wealthy individuals typically returned to the city from their holiday houses, their lighter, whiter floaty frocks were stowed away and replaced with their more formal, dark city attire.

“New York experiences four very contrasting seasons,” NYC-based fashion designer Sylvia Lee told news.com.au. “White fabrics reflect sunlight whereas black absorbs it. It makes sense to wear colours that will keep you cooler in the warmer months.”

“It’s very rare for a cold season colour palette to consist of white unless it is a ‘winter white’ accent colour.”

While it’s not necessarily such a hard and fast rule among the fashion conscious these days, it’s still embedded in American culture today and designers do keep it in mind when creating their latest range.

“As a designer, when I’m choosing a colour palette for spring, I choose very light, pastel colours. For summer, the colours are brighter and more intense. For autumn/winter, they are often darker, deep jewel tones and muted colours,” Ms Lee said.

“Also, during the colder months, when you’re wearing darker coloured leathers, boots, and dealing with rain, snow and unpredictable US weather, it is harder to pair them fashionably with white clothing.

“Having said that, it’s really your choice in the end. I admire anyone who goes against the norm and any rules. Most New Yorkers would agree!”

After all, Coco Chanel was known to wear white as a year-round wardrobe staple, so you who says you have to follow all the rules?