black sheep vs yellow dog

black sheep

noun
  • Used other than figuratively or idiomatically: see black, sheep. 

  • A person who is not wholesome, honest, or trustworthy. 

  • A worker who refuses to strike; a scab. 

  • A nonconformist; an unusual or unconventional person, who may be rejected or disdained by others for this reason. 

yellow dog

noun
  • Used other than figuratively or idiomatically: see yellow, dog. 

  • An item or person of low value. 

  • A Carolina dog. 

How often have the words black sheep and yellow dog occurred in a corpus of books? (source: Google Ngram Viewer )