Dan Zehr wraps up the prequels with his look at the themes in ROTS:
Much can be said of Palpatine’s duality, which becomes personified once he is transformed cosmetically in his chambers during a fatal duel with Mace Windu. The lightning deflected from Mace’s purple blade disfigures Palpatine into a hideous monster. While Palpatine face is scarred, it is merely a representation of the twisted psyche of the future Emperor of the Galactic Empire. He changes before Anakin from a kindly, wise, human mentor, into a tour de force of evil. This outward change is merely a facade, to mask the duality of the individual. This dual nature helps Palpatine wreck havoc on the unsuspecting galaxy.