It was then that I remembered the colour blue, the blue of the sky in nice that was at the origin of my career as monochromist. I started work towards the end of 1956 and in 1957 I had an exhibition in Milan which consisted entirely of what I dared to call my 'Epoque bleue'.
In 1957; p. 31 - "Yves Klein, 1928 – 1962, Selected Writings"