"As white as a ghost" or "as white as a sheet" means that someone has lost the color from their face because they are scared or frightened. For example: She trembled with fear and was as white as a ghost.

Also, you may say: As white as snow.

"As white as a ghost" is an idiom. If someone looks as white as a sheet or as white as a ghost, they look very pale because they are frightened or because of illness or shock. For example, "The thief was as white as a ghost when a policeman came near him"

就是白到像鬼一樣的意思:)