midnight blue vs woad

midnight blue

noun
  • a dark blue colour, almost black. 

adj
  • of a dark blue colour, almost black. 

woad

noun
  • The blue dye made from the leaves of the plant. 

  • The plant Isatis tinctoria. 

verb
  • To plant or cultivate woad. 

  • To dye with woad. 

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