This volume gathers twenty-five texts of the Norwegian physicist Torger Holtsmark. Most of them document his lifelong occupation with the problem of colour. They are contributions to colour theory and optics where Holtsmark picks up and develops research trajectories ranging from Plato and Aristotle via Kepler to Goethe and Wittgenstein. Underlying his interest in the historical context, one always finds the question as to the genesis of image, the determination of colour and the fate of the 'seer'. The answers that Holtsmark finds lead him to demand a novel comprehension of the theory of light and, in a practical way, to forge a didactic design for an extended theory of colour as a theory of images.