filthy vs off-colour

filthy

verb
  • To make very dirty; to saturate something with dirt. 

  • To cover in filth. 

adj
  • Covered with filth; very dirty. 

  • Obscene or offensive. 

  • Very unpleasant or disagreeable. 

off-colour

How often have the words filthy and off-colour occurred in a corpus of books? (source: Google Ngram Viewer )