If I understand this correctly, the late NY singer Laura Nyro used something similar in technique way back in the cusp of the 1970s-and maybe later. She could not read or write a note of music-but could complete the basic structure of her song/melody on her piano.
She used to fill out the rest of the song to completion by telling her producer:

"I think we need a little green in this section, and at the end something like yellow"
It used to drive him crazy, but he finally got to understand her meanings, and would hire a harpist, bass player, saxophonist 12 string guitarist as the 'color' dictated and she usually approved etc...

(not to diminish your app,(way before there were apps) just interesting that this was her way of describing music via free-form association)
As you might guess I am a fan