bicolour vs polychromatic

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. 

polychromatic

adj
  • Showing a variety, or a change, of colours; having many colours; multicoloured. 

  • Composed of more than one wavelength. 

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