The color began appearing in Western art in the Middle Ages ... During his well-known early Blue Period, a young, impecunious Picasso painted people on the margins in somber, saturated blues.

Another source was Matisse’s Blue Nude (Souvenir de Biskra) (1907) and the shock and pose of its misshapen subject. Later that year, the artists exchanged paintings. Picasso chose a portrait of ...