Some of the chords in the song "Something Entirely New" are the same as other fusion songs in the series like "Giant Woman," "Strong in the Real Way," and "Stronger than You."
Blue Diamond will eventually be voiced by Lisa Hannigan. But this flashback story is told in narration, so Estelle (Garnet) provides all the voices of characters that have not yet been seen before.
Estelle is occasionally credited incorrectly as the voice of Blue Diamond in this episode; The episode is told in flashback to Steven from Garnet's point of view, so everything Blue Diamond says, Garnet tells Steven she says. Estelle voices the character telling the story, Garnet, not Blue Diamond. As of yet there is no confirmed voice actor for Blue Diamond.