People are shocked to discover the secret power of red underwear

Fashionistas are no longer seeing red thanks to this surprising wardrobe hack.

Wearing red undergarments beneath white clothing can make them appear nearly invisible, according to color theory — and the seemingly counterintuitive styling trick that has shocked shoppers across TikTok.

Australia-based TikTok user Elizabeth Zemlyanoy put her red briefs to the test in a viral video earlier this year.

The shock written on her face says it all: the cherry-hued boyshorts were utterly invisible beneath the snug-fitting white trousers.

“I was today years old when I found out you can wear red undies under white pants,” the 20-year-old captioned the clip, which racked up more than 43,000 views.

Wearing such vibrant underwear under white garments, no less, seems counterintuitive — firetruck red should, in theory, be a glaring eyesore beneath the barely opaque garments.

In another recent viral video, UK beauty influencer Lydia Rose demonstrated the stark difference between red and white bras underneath a white tee, vowing to ditch her plain panties for good.

“Cute red underwear from here on,” she wrote in the caption.

Her followers, however, weren’t sold.

“Skin tone is best… whatever that shade is for you,” declared one viewer.

Advised another. “If you don’t want to see the bra, it needs to blend in with your skin because that will be the color showing through your tops.”

“Wear red under the sun, let’s see if it’s the same,” one skeptic quipped.

While skin-colored sets have long been the shade of choice for wearing beneath white, color expert and Fashion Institute of Technology professor Jada Schumacher broke down the optical illusion.

“Many of the nudes available are a sort of synthetic, light skin color, which is too pasty for most people,” she told Wirecutter, owing to why beige bras may stand out against darker skin tones.

Red, on the other hand, is “in the dead middle of the [color] value spectrum.”

But not all reds are created equal — the key to finding the perfect hue is matching it to the wearer’s undertones.

Schumacher said the red set must have the same lightness or darkness as the skin tone.

Even when attempting to find an ideal match, some of the burgundy bras fell flat.

A SELF staffer learned the hard way: her somewhat pink-tinted undergarment peaked through the white tee.

“To make this trick work, you’ll have to look for a bra that’s a true red, or a deeper one, like burgundy, and stay away from fuchsia or hot pink tones,” wrote SELF contributor Jessica Cruel.