In devotional pictures of the Quattrocento by Giovanni di Francesco Toscani, Fra Angelico, Zanobi Strozzi, Benozzo Gozzoli, and Bartolomeo Caporali, floor and wall fields repeatedly appear as non-representational color grounds. They refer to a hitherto rather insufficiently analyzed multi-layered reflection of the design modes of the time. These surfaces only superficially resemble natural stone structures. Rather, they are coloristic