The oil painting »Bildarchitectur rot gelb blau«, 1923, [Pictorial architecture red, yellow, blue] is one of the »square pictures« that Paul Klee worked on during his time at the Bauhaus in Weimar, and which he systematised in his Dessau Bauhaus period (1927-1930). More than ten years earlier, Klee had composed his first watercolours out of coloured geometric shapes, and he had later transferred the principle into poetic variations. The »square pictures« of the Bauhaus period are among the few completely non-representational compositions in Klee?s oeuvre, and they bear witness to his systematic work on the theory of colour.