The figure shows how geometrical music theory represents four-note chord-types -- the collections of notes from a tetrahedron, with the colors indicating the spacing between the individual notes in a sequence. In the blue spheres, the notes are clustered, in the warmer colors, they are farther apart. The red ball at the top of the pyramid is the diminished seventh chord, a popular 19th-century chord. Near it are all the most familiar chords of Western music.
 
Image: Dmitri Tymoczko