* Detail from Vincent van Gogh's 'The Sower', 1888 with van Gogh's letter to his brother Theo, Arles, c. 21 November 1888 "...Here’s a croquis of the latest canvas I’m working on, another sower. Immense lemon yellow disc for the sun. Green-yellow sky with pink clouds. The field is violet, the sower and the tree Prussian Blue." Picture: Van Gogh Museum