The following article contains an answer for the question: What is the full name of the person who said that "rather than being a decorative element, [Messiaen showed that colour] could be a structural, a fundamental element"? , can you please find it? 

Colour lies at the heart of Messiaen's music. He believed that terms such as "tonal", "modal" and "serial" are misleading analytical conveniences. For him there were no modal, tonal or serial compositions, only music with or without colour. He said that Claudio Monteverdi, Mozart, Chopin, Richard Wagner, Mussorgsky and Stravinsky all wrote strongly coloured music.In some of Messiaen's scores, he notated the colours in the music (notably in Couleurs de la cité céleste and Des canyons aux étoiles...)—the purpose being to aid the conductor in interpretation rather than to specify which colours the listener should experience. The importance of colour is linked to Messiaen's synaesthesia, which he said caused him to experience colours when he heard or imagined music (he said that he did not perceive the colours visually). In his multi-volume music theory treatise Traité de rythme, de couleur, et d'ornithologie ("Treatise of Rhythm, Colour and Birdsong"), Messiaen wrote descriptions of the colours of certain chords. His descriptions range from the simple ("gold and brown") to the highly detailed ("blue-violet rocks, speckled with little grey cubes, cobalt blue, deep Prussian blue, highlighted by a bit of violet-purple, gold, red, ruby, and stars of mauve, black and white. Blue-violet is dominant").When asked what Messiaen's main influence had been on composers, George Benjamin said, "I think the sheer ... colour has been so influential, ... rather than being a decorative element, [Messiaen showed that colour] could be a structural, a fundamental element, ... the fundamental material of the music itself."

George Benjamin