Stains on marble can usually be bleached out with the aid of ammonia and a paste made up of hydrogen peroxide and whiting powder. First, wash the stain with ammonia and rinse. Then spread the paste on the stain and sprinkle on a few drops of ammonia.
Cover the paste with a piece of polythene to help keep it moist. And leave it for a few minutes. Then wipe off the paste, rinse the marble thoroughly with plenty of hot water, and repolish the area.