I think you’re not talking about actual red rooms. The concept of red rooms aren’t really new or unique. Red rooms are like an urban legend of a room where people pay to watch others be tortured and snuff stuff on the dark web. The real life existence of them has been argued about for a long time. Not to be confused with play rooms which are real and you can find reddit threads of people showing off their play rooms for bdsm online. A common wall paint colour for these rooms is red. It’s a place for bdsm people to set up scenes and store all their equipment. For some reason a lot of bdsm people just like painting the whole room red floor to ceiling and then have like lines and lines of black leather equipment and furniture. I feel that probably what inspired both stories moreso. Fifty shades of grey had a similar room too iirc
Spoiler alert for whoever's gonna see
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Jiwook found Juyeon pretty back then, he just couldn't accept that he like guys bc of his internalized homophobia, so he abused and raped him instead. And when he was doing so, he also put red lipstick on Juyeon's lips, so that's how the color red become traumatizing for Juyeon, now he use it for jiwook to remember the past, but he still hasn't.

I just listened to a podcast of this book and there's a Red Room in there as well. Everything in that room is painted red. From the floors, walls, and all the way to the ceiling. Then each side of the walls has a painting of women covered in bruises which signifies domestic abuse. I was wondering if the room in this manhwa was influenced by the same room from this book. Creepy...