The harmony for All the Things You Are seems mostly straightforward, but I'm stuck on a few bars struggling to see where the following non diatonic chords come from. The chords are: C+7 in bar 24, D♭m7 in bar 30, and B°7 in bar 32. All help much appreciated. Thanks.
This is one of the most brilliant and fun to analyze songs from the American Songbook. One would think with the number of modulations there are in this song it would sound very technical but the melody combines with the harmony to make it a lyrical and harmonic masterpiece.
Bar 24 C+7 is a dominant V7 of the Fm7 (VIm7) chord in bar 25.
Bar 30 Dbm7 is a IVm7, borrowed from the parallel minor of the key of Ab.
Bar 32 Bo7 is a bIIIo chord used as a chromatic passing chord from the IIIm7 in 31 to the IIm7 in 33:
Cm7 Bo7 Bbm7
So you’re ok with the rest of the song? There’s a lot going on there!