From William Rubin, "Picasso in the Collection of the Museum of Modern Art":
"Blue dominated Picasso's palette and hence the mood of his subjects from the end of 1901 until late 1904. His friend Jaime Sabartës recalled that "a mound of white in the center [of the palette] constituted the base of a kind of cement composed mainly of blue. The other colors formed its border."
"The use of a single hue to create a mood, a hue that floods the picture and usurps the local colors of objects, was essentially a Symbolist device. Thus it relates Picasso's work in these years to late nineteenth-century art more than to contemporary explorations of color such as in the work of the painters then gathering around Matisse, who were soon to be known as Fauves.
"Whistler and later, near the turn of the century, Monet had painted blue pictures which, like their other monochrome works, evoke an ambience of isolation, emptiness and reverie. These images approximated the moods of the Symbolist poets, particularly of Verlaine (one of Picasso's favorites), who in L'Art poetique called for an art of nuance rather than color. A number of Cezanne's later pictures, which were also painted in gradations of blue, have affinities with Symbolist painting and even more closely anticipate Picasso, insofar as some were portraits and figure pictures while the Whistlers and Monets were largely uninhabited landscapes.
"Except for the appropriation of the basic Symbolist device, however, the "Blue Period" paintings have little in common with late nineteenth-century prototypes, for Picasso associated the mood-color in a very literal way with a particular cast of characters: lonely, suffering, poverty-stricken outcasts from society (a subject matter favored by his Barcelona friend, Isidre Nonell, whose studio Picasso had borrowed for a while just before 1900). Beyond the humanitarian sentiments they imply, these subjects have been considered symbols of Picasso's penurious situation at the time; his sales had fallen sharply after the Vollard exhibition, and mere survival had become difficult. But the narrowing to these themes perhaps represented as much an effort to define himself in terms of a characteristic subject matter as it did a commentary on the artist's place - or rather lack of place - in society. To be personal, one had to be sincere; and in Picasso's immediate circle, as Sabartés said, "sincerity... could not be found apart from sorrow." Despite noble intentions, however, it often happened, especially in Picasso's imagined compositions - as opposed to the portraits of his friends, which are firmer and more direct - that such sentiments spilled over into sentimentality."