Using notes outside of a given key to produce heightened color is referred to as

Using notes outside of a given key to produce heightened color is referred to as  "chromaticism".

Chromaticism, in music, the utilization of notes unfamiliar to the mode or diatonic scale whereupon an organization is based.  

Chromatic tones in Western craftsmanship music are the notes in an organization that are outside the seven-note diatonic (i.e., major and minor) scales and modes. On the piano console, the dark keys speak to the 5 chromatic tones that don't have a place with the diatonic size of C real; high contrast keys together mean the chromatic size of 12 tones for every octave.

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