water-color vs watercolour

water-color

watercolour

verb
  • To paint using watercolour 

noun
  • This kind of painting as a genre. 

  • A water-soluble pigment. 

  • A painting made by using such pigment. 

adj
  • Pertaining to the methods or products of watercolor. 

How often have the words water-color and watercolour occurred in a corpus of books? (source: Google Ngram Viewer )