dull as dishwater vs monochromatic

dull as dishwater

adj
  • Boring; ordinary; exceedingly dull. 

monochromatic

adj
  • Plain, dull, lifeless. 

  • Having only one color, represented by differing hues and tints. For example shades in a black and white television. 

  • Perceptive of only one color; unable to distinguish colors; total color blindness. 

How often have the words dull as dishwater and monochromatic occurred in a corpus of books? (source: Google Ngram Viewer )