The parallel between the incarnation of the Word and the materialization of the picture may have contributed to the emergence of the legend that St Luke was the painter of the Virgin. When the saint painted a colourful, i.e., lifelike portrait of the Virgin and her child, he brought to life the incarnate Word authentically, hence proving the truth of incarnation. Some depictions of St Luke the painter clearly suggest that the saint's work assumed its materiality as a result of incarnation, upon the intervention of the celestial sphere. Colour is one of the tokens of reality; in several cases it is colour that the physician-painter owed to the heavenly sphere. These include the illustration in Johannes von Troppau's evangeliarium, and the representations of the painting saint in which an angel helps Luke to grind pigment. Rogier van der Weyden's St Luke paints a portrait of the Virgin which is on a par with the old akheiropoietos of miraculous genesis. The same intention is detectable in Jan van Eyck's Holy Face representation.