Borrowed chords and modal interchange, by ear

C major and C minor share a tonic. Borrowing takes a chord from C minor and plays it in C major. F minor is iv in C minor; in C major it brings in A♭, and the key turns wistful for a moment without going anywhere.

From the parallel minor: iv, ♭VI and ♭VII. From Mixolydian: ♭VII. From Phrygian: the flat II, often called the Neapolitan. Each brings in one or two notes of its source scale, and those notes are the colour.

How strong a borrowed chord sounds depends on how far its source is from home. Mixolydian and Lydian differ from major by one note, so their chords are a mild shift. The parallel minor differs by three, so its chords sound darker. Tonalia names the nearest source a musician would give, so F minor in C major is borrowed from C minor rather than from a more exotic scale that happens to contain it.

Each major key has a page with every borrowed chord, grouped by the mode it comes from, nearest first.