Here is a really clear and scientific look at Chromaticism.
     These 4 processes can be applied individually or simultaneously.

Chromatism always -
     (a) operates in the direction of the Voice-leading of a given Orbit:
          if a note resolves downward, it will be flattened;
          if a note resolves upward, it will be sharpened;
     (b) requires the necessary "space":
          if a note resolves a whole tone, chromaticism is possible;
          if a note resolves only a semi-tone, chromaticism is not possible;
     (c) makes a chord more complex;
     (d) makes a chord more powerful;
     (e) produces an irreversible result:
          once a note (or chord) is chromaticized, it stays chromaticized.
A chromaticized note always bears the same note name as the original diatonic note.
All of these properties of chromaticism will become clearer as we see examples.