Havnt seen it... YET, but that's a decent plot twist.
It makes the inevitable bad guy speech "we're the same blaa blaa blaa, join me", better. As for if it's in keeping with personality... Maybe it's symbolic of a pearl of wisdom or something, so then it would be a 'eating an apple from the forbidden tree of knowledge' reference, which makes sense for an intellectual character?
I'm reaching.
Maybe anything is excusable if it's done for Princess and Country?
As for music, Sia's 'Rainbow' was okay, but wasn't amazing or anything.