Jacob Christoph Le Blon, Head of a woman, 1725.

According to Le Blon, three-color printing could reproduce "all the degrees of lights and shades" found in the flesh tones. Lifelike modeling of skin tones was considered the most difficult aspect of reproduction.

Source: From Coloritto, or the Harmony of Coloring in Painting . . . (London, n.d. [1725]), plate 3, after page 27.