From the 1950s, Constant was increasingly interested in architecture. In 1952, in collaboration with the architect Aldo Van Eyck, he created the project Een ruimte in kleur (“A color space”), which was exhibited at the Stedelijk Museum of Amsterdam. The book, Voor een Spatiaal Colorisme, published in conjunction with the show, illustrates the principle of “spatial colorism” advocated by Van Eyck and Constant in a reaction to the passive role of color in modern architecture. Opposed to the subordination of color to form, they called for an active collaboration between painter and architect to think together in the same movement. According to them, in a vein inherited from Dutch neoplasticism of the 1920s, form and color must work together to create a “color space” (ruimte-kleur). In Constant’s painting, the expressive gesture of the COBRA period disappears, henceforth being defined in a spatial plasticity close to the principles of De Stijl. From 1953 on, the artist experimented with his research on spatial colorism in three dimensions, in particular through sculpture.