aqua vs indigo

aqua

adj
  • Of a greenish-blue colour. 

noun
  • A shade of colour, usually a mix of blue and green similar to the colour turquoise. 

  • The compound water. 

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). 

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