mottle vs stipple

mottle

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

noun
  • A distinguishing blotch of color. 

  • A mottled coloration or pattern. 

stipple

verb
  • To use small dots to give the appearance of shading to. 

noun
  • The use of small dots that give the appearance of shading; the dots thus used. 

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