What are the different ways of adding non-diatonic chords?
I'm trying to add more detail to what I'm playing by using non-diatonic chords. So far the main ways I have found are: 1. Borrowing chords from parallel key (mode mixture) 2. Chromatic Mediants (playing major chords that are minor thirds apart from example). 3. Using Secondary Dominants. Are there any other ways?