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 protoforms of the pictorial figurations, which is why these color fields, apart from a theological sub-iconography, can also be understood as references to the substrate character of the color. By evoking spiral and snail shapes in addition to completely amorphous spots, they also seem to reflect the processes of rock formation as explored in Albertus Magnus’s De mineralibus . As a fluid matter that can develop spontaneously into any form in the sense of a painterly generatio spontanea , color finally approximates the Aristotelian concept of hylē . This contribution seeks to explore the exciting and dynamic relationship between matter and form in the quattrocentesque devotional picture. The color substance of the amorphous grounds is understood as an activated source material that is transformed into vivid forms by way of the respective artistic technē .