I've run into a couple songs recently that use two keys at the time, but not in the way that would meet the definition of polytonality.
What they do is they establish one key as the primary key and then blend in a second key but don't change to that key. They'll use it for a riff or a couple measures, or the song will take the groupings of notes that make up both scales and use them as if they are one scale.
I did some research on this but the best thing I could find is polytonality, and based on what I've read and the videos I've watched this doesn't seem to meet the definition of polytonality.
So would this be considered polytonality? If not, what would this be considered?
One example is a song called "Coloring Book" by a Kpop group called Oh My Girl. The song is in E Major, it blends in E Minor in the chorus, but doesn't change to E Minor, it just kind of uses it.