Patrick Stewart said in an interview that when he finished reading the script at his country home in England, it was so terrifying that he locked up his house, turned on the security system and poured himself a Scotch. He then knew that he wanted to play the Darcy Banker role because a character that horrifying would be an incredible challenge and make for a compelling film.
Jeremy Saulnier wanted to make this film partly because as his career advanced, he knew he would not be offered the chance to make a film as ultra-violent and bleak as "Green Room" and that no novice filmmaker would be given the chance to direct it either. He felt that after the success of "Blue Ruin" the time was right to take on a film as demanding as "Green Room."
During a 2015 Q&A at Fantastic Fest in Austin, TX; Jeremy Saulnier confirmed that while his last two films had colors in the titles- Blue Ruin (2013) and Green Room (2016), he wasn't really working with color as a theme. Rather, Saulnier joked, Green Room was part of his "inept protagonist trilogy" wherein the protagonists are in over their heads and trying to survive using skills they don't really have. This theme is present in both Blue Ruin and Murder Party (2007).
While the tracks were recorded separately than when they are seen being played, the actors actually performed their songs. Anton Yelchin and Alia Shawkat already knew how to play their instruments, but according to director Jeremy Saulnier actor Callum Turner had no experience with any sort of music. Joe Cole also learned to play drums specifically for this film.
Emily is stabbed in the head (left temple) exactly in the same way Dwight Evans kills Wade Cleland in Blue Ruin (2013). That scene is quite gory, bloody and messy, which makes the comment of the band about Emily possibly not being dead because of the lack of blood somehow funny and a subtle cross reference to the movie.