Tactical urbanism is the strategy behind testing new uses for streets and public squares before committing to permanent changes. Colour plays a crucial role here—it's the simplest way to make these transformations visually unmistakable. Milan has embraced tactical urbanism with remarkable success, as demonstrated beautifully in Piazza Dergano. Photo: (c) Demetrio Scopelliti

Coloured corner of Vienna's Parliament building: Architect Theophil Hansen fought tirelessly to paint the facades of his neoclassical Parliament in authentic ancient colours. In doing so, he became a central figure in the 19th century's fierce "polychromy debate"—while antiquity inspired neoclassical architecture, fierce disagreement raged over whether buildings should actually be painted in historical colours. Ultimately, Hansen was permitted only to test his colour scheme on a single corner of the façade. What was once hotly contested is now meticulously preserved. Photo: (c) Herzi Pinki, CC BY-SA 4.0 Deed

Colourful façades on Otto-Richter-Straße in Magdeburg. "We will no longer build or accept colourless houses," declared Bruno Taut in his 1919 manifesto "Call for Colourful Building." When appointed city planning officer of Magdeburg two years later, he seized the opportunity to realize his vision. The grey city transformed almost overnight into a riot of colour that astonished residents and critics alike. The 1922 city guide—published for the MIAMA exhibition (Central German Exhibition for Housing, Social Welfare and Labour)—showcased roughly one hundred painted houses to an international audience. Photo: (c) Magdeburger Platte