Hi Bob M, I'm not a pianist so I think I can give you a lay person's ultra-simple take on Joni piano chords. If you string the basic notes along: c, d, e, f, g, a, b, c -standard chords are based on thirds. the first note being the root of the chord. Take every other note and you've got a simple chord: ceg for example. Usually the root chord, c here, would also be played in the bass as well: cceg. Joni likes to add notes to the root chord, or substitute notes (suspend notes) , and/or add or change the base note. The new notes change the tone and character of the chord. In Paprika plains, the basic "add on" to the root chord of the song is a D note replacing the c. So the simplest home chord of the song is cdg. It's a simple variation on Joni's favorite open chord. Lots of her open tunnings are variations on C.
There is a basic fingering to piano chords, so changing the fingerings opens the tuning, so to speak. What's remarkable is that Joni can resolve the added notes as the melody plows along. --Well, mostly. When Joni toured BSN in Chicago, we stopped one of the musicians afterwards and asked what it was like performing with Joni. He said it was a dream come true, except everyone was worried because all the notes were wrong and they they all felt they were playing the music incorrectly the entire time. Maybe that Christmas cd will be brimming with piano tunes. She likes change. -That would be a change.
