Kristen Bell had to darken her hair to look "bad".

The actress stars in new movie 'Burlesque' and producers asked her to alter her appearance as they didn't think she looked convincingly evil enough for the role.

He said: "I'm a blonde girl who goes dark to go bad. They felt my character should be brunette and bad."

Kristen - who recently got engaged to Dax Shepard - stars in the film with singers Cher and Christina Aguilera and loved playing a nightclub worker who got to bully the 'Dirrty' hitmaker.

She added to the Daily Mail newspaper: "I'm the girl who feels threatened by Christina.

"It was make believe - I just pretended to make Christina's life a misery."

Kristen recently revealed she was star-struck when she first started filming with Cher.

Kristen - who plays dancer Nikki - said: "Cher owns the club and we play best friends, I'm her lead dancer and Christina sort of comes in between the two of us and I'm not very happy about that!

"I could talk but I was definitely having to take a breath and I was going, 'I'm in a room with Cher right now', but she's so personable and down-to-earth, it's not really what you expect, she's very easy to be around."