polychromate vs rainbow-colored (US) / rainbow-coloured

polychromate

noun

  • A salt or ion composed of multiple chromate groups 

adj

  • Composed of many colours 

rainbow-colored (US) / rainbow-coloured

How often have the words polychromate and rainbow-colored (US) / rainbow-coloured occurred in a corpus of books? (source: Google Ngram Viewer )