mottle vs unspot

mottle

noun
  • A distinguishing blotch of color. 

  • A mottled coloration or pattern. 

verb
  • To mark with blotches of different color, or shades of color, as if stained; to spot; to maculate. 

unspot

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