It's like she's playing notes which are revealing themselves as visible colors, just like synesthesia. And of course the shading is awesome. I've been learning what I can from your tutorial you put up recently so I can become as good at shading as you.
Great pic overall. But I'm gonna be that one guy to point out something wrong. At the end of the bow, there's a little nob that turns to tighten or loosen the hair by moving the frog (the grey part in this picture). [link]