Ultramarine
A small addition of zinc-white (zinc oxide) causes the colour to become less vivid (~bright). Synthetic ultramarine, invented in the 1820s, is very cheap. It is largely used for wall painting, the printing of paperhangings and calico. It is also used to correct the yellowish tinge found in things meant to be white, such as linen, paper, etc. Bluing or "laundry blue" is a solution of synthetic ultramarine (sometimes, prussian blue) that is used for this purpose when washing white clothes. Large amounts are used in making paper, especially the kind of pale blue writing paper popular in Britain. During World War I, the RAF painted the outer roundels with a colour based on ultramarine blue. This became BS 108(381C) Aircraft Blue. It was replaced in the 1960s by a new color based on phthalocyanine blue, BS110(381C) Roundel Blue.