The perception of colour is a gift just as definitely granted to one person, and denied to another, as an ear for music; and the very first requisite for true judgment of Saint Mark’s, is the perfection of that colour-faculty which few people ever set themselves seriously to find out whether they possess or not. […]

The fact is, that, of all God’s gifts to the sight of man, colour is the holiest, the most divine, the most solemn. We speak rashly of gay color and sad color, for color cannot at once be good and gay. All good color is in some degree pensive, the loveliest is melancholy, and the purest and most thoughtful minds are those which love colour the most. 

– John Ruskin, The Stones of Venice 

Ruskin thought about color all the time, and wrote about it often. See for instance this post. He seems to have thought color itself a mystical and revelatory thing, something he was surprised and delighted that God took the trouble to create.