Here is a new way to view the chromatic spiral. I have added circles of colour corresponding to the notes played to enhance the idea of the colour wheel representing the pitch circle. These large circles overlap and blend. The idea is to associate these blended colours we see with the interval of the two notes we hear.
I am not sure if this works. When we have three notes from opposite sides the three opposing colours blend to white. White is the presence of all colours therefore it should be the sound of not only all notes but all frequencies in between.
However, one experiment remains and that is to use the primary colours in the positions of the tonic, third and fifth. Although, as I type this I cannot imagine this working.
Pythagoras is known as the Father of Music formalizing a system built on ratios and came up with the 7 notes of the octave. Over time we have filled in the gaps with the ‘black keys’. When played separately these five notes form the Pentatonic Scale which is found all over the world in largely indigenous music. Bobby McFerrin explains the Pentatonic scale best here: http://www.ted.com/talks/bobby_mcferrin_hacks_your_brain_with_music