Alexander Scriabin was an innovative composer who saw music tonalities as colors. His so-called Mystic chord is a complex polychord that is unique to his oeuvre.

Play "Prometheus" suite

In music the mystic chord or Prometheus chord is a complex six-note scale which loosely serves as the harmonic and melodic basis for some of the later pieces by Russian composer Alexander Scriabin.It consists of the pitch classes: C, F#, Bb, E, A, D. This is often interpreted as a quartal hexachord consisting of an augmented fourth, diminished fourth, augmented fourth, and two perfect fourths. However the chord may be spelled in a variety of ways and is related to other pitch collections.

Scriabin was a Russian composer and pianist who invented the first colour keyboard and notation for lights and colors based on his scale of Synesthetic colors. His symphony 'Prometheus: The Poem of Fire' (1910) was the first composition in history which included notation for lights and colors

Use
Some sources suggest that much of Scriabin's music is entirely based on the chord to the extent that whole passages are little more than long sequences of this chord, unaltered, at different pitches; but this is rarely the case.
More often than not, the notes are reordered in order to supply a variety of harmonic or melodic material. Certain of Scriabin's late pieces are based on other synthetic chords or scales that do not rely on the mystic chord.

Contrary to many textbook descriptions of the chord, which present the sonority as a series of superposed fourths, Scriabin most often manipulated the voicings to produce a variety of melodic and harmonic intervals (in the same manner that a dominant seventh, built on superposed thirds, will deploy intervals of a sixth, fourth, and/or second under inversion)

Fig.3 Image of Symphony Hall at Yale University showing a live performance of Scriabin's "Prometheus-Poem of Fire".
Scriabin's score was faithfully performed, including computer controlled lighting effects rendered according to Scriabin's instructions.