Paul Klee was born in Switzerland, and is considered both a German and a Swiss painter. His unique
style was influenced by movements in art that included expressionism, cubism, and surrealism. In the piece above, Ad Parnassum each blot of color represents a sound. Paul Klee did not have synesthesia but he completed several works that played with the idea, such as Ancient Sound; Abstract on Black. With Ad Parnassum Klee is representing a huge symbolic performance of Apollo, the muses, Mount Parmassus and the doorway in the bottom left as the portal. I believe that the doorway and the top of the mountain are well paired and represented for that are of the same shade of colors in which portrays their connection.
With his piece Ancient Sound; Abstract on Black Klee acknowledges how sounds work through his paint and shades of green. Here Klee understands darker colors represent lower tones in nature and lighter shades represent higher pitch tones. And for this, the viewer has a sense that this squares above are coming out of the painting in a pyramid type of arrangement.