blue angel vs cobalt blue

blue angel

noun
  • A blue flame produced by lighting one's flatus. 

  • A mollusc of genus Glaucus. 

cobalt blue

noun
  • A deep blue pigment derived from cobalt; zaffre. 

adj
  • Of the color of the pigment zaffre. 

How often have the words blue angel and cobalt blue occurred in a corpus of books? (source: Google Ngram Viewer )