coloration vs iridescence

coloration

noun
  • The act or art of coloring. 

  • Ornamental division (also called passaggi, glosas, diminutions. etc.) employing rapid black notes. 

  • A notational device for indicating hemiola through either use of red ink (in mensural black notation) or black noteheads (in mensural white notation). 

  • The quality of being colored. 

  • Political tendency. 

iridescence

noun
  • The condition or state of being iridescent; exhibition of colors like those of the rainbow; a prismatic play of color. 

  • Any shimmer of glittering and changeable colors. 

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