bichrome vs bicolour

bichrome

adj
  • Having two colours 

bicolour

adj
  • Having two colours 

noun
  • A flower, cat etc., that has two colours. 

  • A flag with such colours, consisting of two stripes that are either vertical or horizontal. 

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