indigo vs purpurate

indigo

adj
  • having a deep purplish-blue colour 

noun
  • A purplish-blue colour 

  • An indigo-colored dye obtained from certain plants (the indigo plant or woad), or a similar synthetic dye. 

  • An indigo plant, such as from species in genera Indigofera, Amorpha (false indigo), Baptisia (wild indigo), and Psorothamnus and Dalea (indigo bush). 

purpurate

adj
  • Of a purple colour. 

noun
  • A salt of purpuric acid. 

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