In 1946, Darnell won the starring role in the highly anticipated movie "Forever Amber", based on a bestselling historical novel that was denounced as being immoral at that time. The character Amber was so named because of her hair color, and this is the only major film in which Darnell—normally known for her raven hair and somewhat Latin looks—appears as a redhead. It was the most expensive film so far produced by Fox, and publicity at the time compared the novel to "Gone with the Wind". Darnell replaced British actress Peggy Cummins in July 1946 at a cost of $350,000. Because $1 million had already been spent on production costs when Darnell was brought in, the pressure was intense to make the film a financial success. Her casting was a result of a campaign for stronger roles. Regardless, she was surprised to find out that she had been cast, because she had been intensively rehearsing for "Captain from Castile" at the time. Although she had to give up that role and work with Otto Preminger, she was delighted to play the title role and thought she was "the luckiest girl in Hollywood."