The chaofu, or robe of state, is the most important of the ceremonial costumes of the Qing Court. The two part construction of the robe, with pleated skirt attached to an upper body, derived from early Ming styles of court dress, adapted by the Manchu to suit their own taste. Choafu are rare due to the fact that they were used as burial robes for those honoured to wear them. For that reason, it is also the most common garment depicted in Qing period ancestor portraits.
At the Qing Court the colour blue was the colour associated with rites performed at the Altar of Heaven, South of the Forbidden City, where the Emperor offered sacrifices at the winter solstice and also prayed for rain during the summer months. Blue was also the colour of Manchu princes of the blood from the first through fourth rank.
Compare an example of a dark blue chaopao dated to the the mid 19th century illustrated by R D Jacobsen, Imperial Silks, Ch'ing Dynasty Textiles in The Minneapolis Institute of Arts, Vol I, Minneapolis, 2000, pp 58-9, No 1.