For the concept of Chromatic tonality see posts 263, 336, 334 .
This concept of chromatic shift of a pair of chords is as follows : Let a pair of chords X1->X2 , that are chords of a diatonic scale S. The 3 possible relations of (X1,X2) is chromatic (roots differ by a 2nd or inverse ), melodic (roots differ by a 3rd or inverse ) and harmonic (rotts differ by a 4th or 5th).
Now the chromatic shift preserves this relation of X1,X2 but may take this pair outside the diatonic scale as it shifts by an interval of one semitone or one tone which may not be of the diatonic scale S.
This shift may change the character ofthe chords X1, X2 from major or minor or dimisnhed to another from the types major , minor or diminished.
By continuing this chromatic shift we return again after 1,2, or 3 steps to a pair of chords of the diatonic scale .
Of course it is not only that athe pair of chords are shifting but also the melody theme relating these 2 chords is shifting also to other scales, and after 1,2 or 3 steps returns again to a melody theme of the the initial scale S.
Here are some example in the diatonic scale S=C major
1) X1=Dm X2= G (harmonic relation of X1,X2)
Dm->G
Dbm->Gb
C->F
2) X1=C X2= F (harmonic relation of X1,X2)
C->F
B7->Em
Bb7->Eb
Am->Dm
3) X1=Am X2= C (melodic relation of X1,X2)
Am->C
Abm->B
Gm->Bb
G->Bd
4) X1=Em X2= Am (harmonic relation of X1,X2)
Em->Am
Fm->Bbm
Gbm->Bm
Gm->Cm
ETC
