iridescent vs polychromate

iridescent

adj
  • Producing a display of lustrous, rainbow-like colors; prismatic. 

  • Brilliant, lustrous, or colorful. 

polychromate

adj
  • Composed of many colours 

noun
  • A salt or ion composed of multiple chromate groups 

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