1
general::
Phrase(s): *white as a sheet [and] *white as a ghost; *white as snow; *white as the driven snow
[of someone] extremely pale, as if frightened. (*Also: as ~.) • Marilyn turned as white as a sheet when the policeman told her that her son had been in a car wreck. • Did something scare you? You’re white as a sheet! • Jane made up the bed with her best linen sheets, which are always as white as snow. • We have a new kitten whose fur is white as the driven snow.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Very pale in the face, as in She was white as a sheet after that near encounter. This simile, dating from about 1600, survives despite the fact that bedsheets now come in all colors.
American Heritage Idioms