I heard about this while I was doing research project on the deep Web. There are a few variations, but here's what I found on the Red Room.
The Red Room is a popup that will appear on your screen while either trying to find information on The Red Room, or using the deep Web. It is a red pop-up with Japanese letters that translate to "do you like the red room?", which is read aloud by a child's voice. This feature was inspired a young schoolgirl in Japan to murder one of her peers. Variations of the story include that the person who views the popup will either be killed by some 'demon' or will go insane.
A 'red room' also refers to an onion website with a webcam showing the torture of an 'ISIS terrorist'. This site contains a chatroom where you can input torture commands. I was not able to find any red rooms using any onion browsers, and I didn't want to go too deep, (I don't want the F.B.I at my house) so if they're real, I wasn't able to find one. Personally, I think red rooms are nothing more than legends, but the deep Web holds some crazy stuff, so you never know.