white as a sheet

Related to white as a sheet: along the lines, take a back seat, without a hitch

(as) white as a sheet

Extremely and unnaturally pale, as due to fear or illness. His face went as white as a sheet when he saw the burglar in his house. Do you feel all right? Your face is white as a sheet!
See also: sheet, white
Farlex Dictionary of Idioms.

*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.
See also: sheet, white
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

white as a sheet

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.
See also: sheet, white
The American Heritage® Dictionary of Idioms by Christine Ammer.

white as a sheet

or

white as a ghost

If someone looks as white as a sheet or as white as a ghost, they look very pale because they are frightened, shocked or ill. When I saw him his face was as white as a sheet and he was crying. She was as white as a ghost and trembling all over.
See also: sheet, white
Collins COBUILD Idioms Dictionary, 3rd ed.

(as) ˌwhite as a ˈsheet/ˈghost

(informal) very pale in the face, because of illness, fear or shock: She went as white as a sheet when she heard the news.
See also: ghost, sheet, white
Farlex Partner Idioms Dictionary

white as a sheet

Pale in the face. This simile dates from Shakespeare’s time; he wrote, “And whiter than the sheets!” in Cymbeline (2.2). The term was repeated by Henry Fielding, Frederick Marryat, Artemus Ward, and Thomas Hardy, among many others, and remains current.
See also: sheet, white
The Dictionary of Clichés by Christine Ammer
See also:
  • (as) white as a sheet
  • (as) white as a ghost
  • white as a sheet/ghost
  • be as white as a sheet
  • be (as) white as snow
  • (as) white as snow
  • (as) pale as death
  • (as) pale as a ghost
  • pale
  • pale as a ghost