Theory of Colours
The interest in colored hearing dates back to Greek antiquity when philosophers asked if the color ("chroia", what we now call timbre) of music was a quantifiable quality. Isaac Newton proposed that musical tones and color tones shared common frequencies, as did Goethe in his book "Theory of Colours". There is a long history of building color organs such as the clavier à lumières on which to perform colored music in concert halls. In further support of this notion, in Indian classical music, the musical terms raga and rasa are also synonyms for color and (quality of) taste, respectively.