The room could be differentiated from the other rooms in the lab due to a rainbow mural in its doorway. Despite its purpose, the room itself was actually rather bleak, having plain white walls and hard white flooring. The only other object present in the room, besides a few toys and some lab equipment, was a white table.
In the early years of her life at the lab, Eleven would play in the rainbow room with Eight.
In an effort to retrieve her missing daughter Jane (Eleven), Terry Ives forced her way into Hawkins Lab, threatening the lab's employees with a gun. She eventually made her way to the rainbow room, where she found Jane and Kali playing. However, she was caught by lab personnel before she could take Jane and escape.
According to Kali, one day she went to the rainbow room and discovered Eleven had been taken away.
After reuniting with her mother, Eleven was able to see Terry's memory of breaking into the lab and finding the rainbow room. Through this memory, Eleven was able to find and reunite with Kali.
- The room could be an allusion to how rainbows are sometimes connected to MKUltra; some claim the 1939 film The Wizard of Oz was used in the mind control experiments, especially the song “Somewhere Over the Rainbow” featured in the film. However, there is no evidence to support this claim.
- The rainbow room could also be a reference to the 2010 film "Beyond the Black Rainbow", a film that has many similarities to Stranger Things.