Songfacts®:

• In this song, Britney Spears compares her up-and-down roller coaster love to a mood ring. Mood rings were a short-lived fad of the mid-1970s, which were especially popular with young girls. They featured fake gemstones that were filled with liquid crystals. These special crystals were thermochromic, which meant they changed colors based upon the temperature of the finger of the wearer. The ring came with a color chart that indicated the person's supposed mood.
• The song was co-penned by Jon Asher and songwriter Melanie Fontana at Asher's ARC Studios in February 2015. It caught the attention of Asher's fellow Roc Nation artist DJ Mustard, who produced the track then sent it to Spears. It features on the Japanese edition of Glory.
• The track was originally titled "Mood Swings." Melanie Fontana recalled to Pop Crush:
  
  "I wrote the song with my friend Jon [Asher], who is an amazing songwriter and one of my really good friends. I had an idea: I wanted to write a song called 'Mood Swings.' We started with some melodies and nothing really hit us. So we went down, started to hang out in his kitchen, had something to eat, and he was like 'Mood swings, mood swings…what about mood ring?" And I was like "Oh my God, 'Mood Ring'!" And that's kind of how it happened: basically joking around while we were having a snack in the kitchen. He came up with the title. We were thinking about it, in our minds, as The Chainsmokers featuring Britney Spears. So that was the concept and sound."
• The song was only available in Japan as a bonus track on Glory until May 29, 2020, when Britney made it available onto streaming and download services worldwide.