Looking at the history of synaesthesia, and especially of coloured hearing in the late nineteenth century, there is a remarkable coincidence between the beginning of the scientific study of the phenomenon and the aesthetic interest in it. Nevertheless, scientific research on synaesthesia and literary, musical, or artistic realizations are usually seen as based on opposite models: whereas in nineteenth-century physiology the senses were conceived of as distinct spheres of activity, aesthetic theory and practice are said to celebrate the harmony and the unity of the senses. This article offers a different perspective on the historical interrelation between physiology and aesthetics by demonstrating the common ground of scientific and artistic reference to synaesthesia.