Blindness is a recurrent theme in Picasso's works of this period, also represented in "The Blindman's Meal" (1903, the Metropolitan Museum of Art) and in the portrait of "Celestina" (1903). Other Blue Period works include "Portrait of Soler" and "Portrait of Suzanne Bloch". The Rose Period (1904–1906) is characterized by a lighter tone and style utilizing orange and pink colours, and featuring many circus people, acrobats and harlequins known in France as saltimbanques. The harlequin, a comedic character usually depicted in checkered patterned clothing, became a personal symbol for Picasso. Picasso met Fernande Olivier, a bohemian artist who became his mistress, in Paris in 1904. Olivier appears in many of his Rose Period paintings, many of which are influenced by his warm relationship with her, in addition to his increased exposure to French painting. The generally upbeat and optimistic mood of paintings in this period is reminiscent of the 1899–1901 period (i.e. just prior to the Blue Period) and 1904 can be considered a transition year between the two periods. By 1905, Picasso became a favourite of American art collectors Leo and Gertrude Stein. Their older brother Michael Stein and his wife Sarah also became collectors of his work. Picasso painted portraits of both Gertrude Stein and her nephew Allan Stein. Gertrude Stein became Picasso's principal patron, acquiring his drawings and paintings and exhibiting them in her informal "Salon" at her home in Paris. At one of her gatherings in 1905, he met Henri Matisse, who was to become a lifelong friend and rival. The Steins introduced him to Claribel Cone and her sister Etta who were American art collectors; they also began to acquire Picasso and Matisse's paintings. Eventually Leo Stein moved to Italy. Michael and Sarah Stein became patrons of Matisse, while Gertrude Stein continued to collect Picasso. In 1907, Picasso joined an art gallery that had recently been opened in Paris by Daniel-Henry Kahnweiler. Kahnweiler was a German art historian and art collector who became one of the premier French art dealers of the 20th century. He was among the first champions of Pablo Picasso, Georges Braque and the Cubism that they jointly developed. Kahnweiler promoted burgeoning artists such as André Derain, Kees van Dongen, Fernand Léger, Juan Gris, Maurice de Vlaminck and several others who had come from all over the globe to live and work in Montparnasse at the time.