Between 1886 and 1889, while in Tahiti, Gauguin penned miscellaneous notes on blank pages of a manuscript of Noa Noa, using it almost as an occasional journal.  The English translation of a brief excerpt:

A given arrangement of colors, lights, and shadows produces an impression. This is what we might call the music of the painting.Often you are seized by that magical harmony before you even know what the subject of a painting is, as when you enter a cathedral and are too far away from the painting to make it out clearly. This is where painting is truly superior to other art, for this emotion is aimed at the most intimate part of the soul.