This is an excellent use of the theme, I haven't seen another game use input from your microphone! After lowing the sound sensitivity I was able to roughly get green-yellow-red to do-re-mi and I was able to get through the first few levels just with my voice. Once the projectiles were introduced though I had to use the number buttons. It's very good that you added an alternate option.
I really like the minimal art style and it's very thematic, but it can be a little hard to see. I'm sure there's a way to increase the clarity if you wanted to take the time. Maybe make the edges of the shapes have more dots concentrated there to kind give them an outline? Red notes are also very difficult to trigger alone in my experience, usually if I was hitting red I was also hitting yellow.
Great job!