Why did Marc Chagall change from colour gouaches to black-and-white etchings for La Fontaine’s Fables?

Marc Chagall switched from colour gouaches to black-and-white etchings for his illustrations of Jean de La Fontaine’s Fables because the printing process originally envisioned by his publisher, Ambroise Vollard, could not accommodate the complexity of his colours.1

While Vollard had initially requested coloured illustrations that resembled 18th-century prints, it became evident that Chagall’s work was too intricate for that specific reproduction method, leading the artist to complete the project using black-and-white plates in 1931.1