Helena Ravenclaw is the resident Hogwarts ghost. Known better as "the Grey Lady", she has a pivotal role to play on Harry's side during the Battle of Hogwarts. Playing a ghostly character must be quite a thrill and a challenge to an actor, but it did mean that we never really got treated to the real-life radiance of Kelly MacDonald as a performer.
Fortunately, there are a great many other places we can see MacDonald, including the cult hit "Trainspotting", and her name was already made as an actor before she took the part. Recently separated after a long-term marriage to a Scottish rock star, she's next due to appear in film in "Holmes and Watson" as Mrs. Hudson. As we can see in the second picture, she's more than capable of lighting a screen up when she's shot in color!