This question stayed with Wilson for the rest of his life. He pursued it from multiple perspectives, beginning with the physiological aspect of colour and progressing to the physical, philosophical, artistic, therapeutic and lastly spiritual aspects. The results of his investigations, which he published in leading scientific and Anthroposophical journals, are presented here together with his monograph for the first time in one volume. Since the chronology of his works happens to mirror loosely the structure of Goethe’s Theory of Colours, “"a Goethean approach to a fundamental problem” is a fitting description of his works on colour as a whole.