7. Julia Roberts
Natural hair color: Blonde
Why she went red: Perhaps Richard Gere said it best in Pretty Woman (1990) when he first beheld Roberts as hooker Vivian out of her cheesy blonde wig:
She says, "Red." He says, "Better." No further discussion.
That's reason enough isn't it? One of Hollywood's most glamorous stars of the '90s went red simply because it was better.