“Color est lux incorporata perspicuo” Robert Grosseteste's Definition of Colour and Its (Franciscan) Legacy

The peculiar definition color est lux incorporata perspicuo (“colour is light incorporated within something transparent”) appears in several writings by Robert Grosseteste and circulated during the central decades of the thirteenth century, especially among Franciscan scholars and in commentaries on Aristotle’s De anima, such as those by Richard Rufus, Geoffrey of Aspall, and so on, and the entire De colore by Grosseteste was copied in Bartholomeus Anglicus’ De proprietatibus rerum and in Roger Bacon’s Liber de sensu et sensato. This chapter intends to examine meaning and sources of this definition and its use in Grosseteste and in the abovementioned masters and commentaries. Finally, it considers its application in an anonymous Tractatus de iride – recently discovered and edited – which combines the definition of colour as incorporated light with Averroes’ theory of the double essence of colour, that is, “‘real”’ in things and “‘spiritual”’ in the medium, for explaining how and why rainbows are coloured.