mottled vs polychromic

mottled

adj
  • Colored in patches; spotted. 

polychromic

adj
  • Polychromatic; many-coloured. 

  • Pertaining to, or designating, any one of several acids (known only in their salts) which contain more than one atom of chromium. 

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