When I listen to music, I see corresponding colors, emphasized Olivier Messiaen once during a talk, and he thus summarized what he repeatedly tried to explain: These are wonderful and undescribable colors of extraordinary diversity. Just as sounds stir, change, and move, in correspondence these colors move in constant metamorphoses. For Messiaen, there existed an immediate link between sets of sounds (modes, chords) and color combinations which he described in great detail. His color-sounds (les sons-couleurs) were of utmost importance to him: Based upon his deep religious belief, Messiaen was of the opinion that color music—similarly to church windows of the Middle Ages—helped to overcome conventional perception to bring about a state of being blinded that ultimately lead to faith.
He also compared Couleurs de la Cité céleste (Colors of the Celestial City), a composition for piano, wind, and percussion, to the “rose window of a cathedral in flaming and invisible colors.” Inspired by the biblical Apocalypse (Revelation of St. John), Messiaen created this work in 1963 and worked among other things with Indian and Greek rhythms, Gregorian themes, bird songs, and of course with color-sounds. In a composer’s note, he wrote: The form of this work is entirely determined by colors. The melodic and rhythmic themes, sets of tones and timbres, develop just like colors. […] Sound-colors, for their part, are symbols of the Celestial City and of Him who lives there.
Messiaen notated the corresponding names of colors on the score of Couleurs de la Cité céleste. He had done this once previously, in his orchestral work Sept Haïkaï (in the 5th movement) from 1962. Together with Chronochromie (1959/1960), these compositions represent a highlight of his creative interaction with the possibilities provided by color music.
 Speech on the occasion of the Erasmus award ceremony, 1971, quoted from Aloyse Michaely, Die Musik Olivier Messiaens. Untersuchungen zum Gesamtschaffen, in Hamburger Beiträge zur Musikwissenschaft, special edition, Hamburg: Verlag der Musikhandlung K.D. Wagner, 1987, 214.
 On the 3rd mode, 2nd transposition he noted for example: Horizontal color ribbons layered on top of each other: from bottom to top dark gray, mauve, light gray, and white with mauve and light yellow reflexes—imprinted with bright, golden letters of an unknown language and many, very tender, hardly visible red or blue curves respectively. Predominant colors: gray and mauve. Quote and illustrations in: Thomas Daniel Schlee, Dietrich Kämper (eds.), Olivier Messiaen. La Cité céleste—Das himmlische Jerusalem. Über Leben und Werk des französischen Komponisten, Cologne: Wienand, 1998, 162–163.
 Quoted from: Michaely, Hamburger Beiträge zur Musikwissenschaft, 1987, 233. At the end of the foreword you will also find Messiaen’s comparison to the rose window.