The Last Supper by Leonardo da Vinci is, of course, the central focus of the prestigious refectory that houses it. However, the conservation of the painting depends on a complex system of environmental control and pollutant filtration, the development of which required long studies lasting twelve years. The possibility of appreciating the unprecedented chromatic qualities and the extraordinary refinement of the details that emerged after the restoration carried out by Pinin Brambilla Barcilon also depends greatly on the lighting conditions of the surrounding environment. Our company was commissioned by the Italian Ministry of Cultural Heritage to collaborate with the Istituto Centrale per il Restauro and with the experts of the Superintendence for the design and realization of the colours of the refectory. These colours immediately proved to be particularly critical, both because they had to “dialogue” in terms of tone, transparency, and surface texture with the painting, and because they had to ensure an appropriate reflection of the lighting system specially designed by Achille Castiglioni. Several months of work were required to identify the most suitable intervention technique and to define the final colours. The execution was then carried out by our restorers and colour specialists, who were specifically trained to work in coordination on the large surfaces of the walls and the ceiling vaults, which are now characterized by refined semi-transparent finishes.