Ostwald developed a strong interest in color theory in the later decades of his life. He wrote several publications in the field, such as his "Malerbriefe" ("Letters to a Painter," 1904) and "Die Farbenfibel" ("The Color Primer," 1916). His work in color theory was influenced by that of Albert Henry Munsell, and in turn influenced Piet Mondrian and other members of De Stijl and Paul Klee and other members of the Bauhaus school. Ostwald's theories also influenced Americans Faber Birren and Egbert Jacobson.