The White Devil is the title of the play—but the term "white devil" isn't actually used in the text of the tragedy. Who is the "white devil" anyway? Is it Vittoria? That seems like the strongest possibility—she does a better job of presenting her goodness than Flamineo or Brachiano do, while remaining essentially guilty. Or maybe it refers to any of the characters in the play who use a veil of deceit to hide their evil deeds? The idea that the color white symbolizes purity is used in other ways during the play though. After Flamineo murders his brother, Cornelia asks him:
Will you make me such a fool? here 's a white hand:
Can blood so soon be washed out? (5.4).
The implication is that it can't—sin runs deeper than any pretence of goodness.