To preserve the sense of the 'grey' even in the most powerful green is amazingly difficult and whoever discovers it will be a happy mortal. (translation from the Dutch original: Fons Heijnsbroek)

letter (July 1860) to his maecenas Johannes Kneppelhout; as cited in Dutch Art in the Nineteenth Century – 'The Hague School; Introduction', by G. Hermine Marius, transl. A. Teixera de Mattos; publish: The la More Press, London, 1908