n May 1957, Yves presented a double exhibition: one part at Iris Clert gallery: Yves, Propositions monochromes, May 10-25; the other part at the Colette Allendy gallery, Pigment pur, May 14-23.
At Iris Clert’s, Yves chose to present the Monochrome Propositions as he had shown them in Milan. The advent of the Blue Period was celebrated by the release of 1,001 blue balloons into the Paris sky during the inauguration. Klein referred to the gesture as a Sculpture aérostatique (Aerostatic Sculpture).