Thank you for playing, I'm glad that you enjoyed it!
Knowing musical notation technically doesn't matter for this game. The notes that you play do show up on screen, but you are not required to know if the note is "F" (or in the case of solfège for F major, "Do"). It is just there as a visual aid to help see the progression of pitches that the player inputs. Even the rhythm test of the melody has a scale below that shows the controls for each note, so in the case that the player completely forgot what notes they played to unlock that melody, they can visually match it up using that diagram. No need to know what the notes are called or anything (though familiarity definitely helps I would imagine).
I think that the visual impairment mode is a great idea and is wonderful that you included it in your game! For mine, a person needs to hit [START] or [A] twice before getting to the game, but after that, no visuals are needed! There are auditory cues that suggest progression to a new scene. However, for the rhythm test part, I should probably make the downbeat on the metronome sound effect be a unique indicative tone. Otherwise, this game was made with the idea of purely receiving necessary information through audio.
PS - nice lime green GameBoy!!