Reading Eco's Art and Beauty in the Middle Ages, a short written in the 1950s, something startling starts to take shape. In Grosseteste in the 12th century (Eco uses the Hexaemeron, not the de Luce), light is the processual unity of creation. In Aquinas in the 13th, the light is beginning to break up into its realia. What seems apparent is that the mediaeval allegorists respond to this fragmentation with an ossification and sytematisation of the culturte of signatures noted in The Order of Things. The fragments whose symbolic analogies linked them back to creation were in danger of multiplying beyond order, of creating an excess of meaning. In order to regularise them, and prevent the swamping of meaning in its own excess, the kind of systematic allegory exemplified by the Romance of the Rose anchors them in a formal arrangement whose ambition is radical completeness. That it couldn't be achieved is clear from the 12,000 lines Jean de Meun added to Guillaume de Lorris' work half a century before.
Before the Romance, to take an arbitrary and extended moment of literary history, and probably some time before, even earlier than its formal expression in Grosseteste, lies a lost unity. In its place, there emerges during the period of transition from feudal to guild systems (and Gimpel's 'mediaeval industrial revolution) an iteration of the theory of proportion, now in an early, one might say pre-mathematical mode.
From this vantage point it begins to be possible to descry the genealogy of hexadecimal colour.