Blue is the color of the clear sky and the deep sea. On the optical spectrum, blue is located between violet and green

Blue pigments were made from minerals, especially lapis lazuli and azurite. These minerals were crushed, ground into powder, and then mixed with a quick-drying binding agent, such as egg yolk); or with a slow-drying oil, such as linseed oil, for oil painting. To make blue stained glass, cobalt blue aluminate: pigment was mixed with the glass. Other common blue pigments made from minerals are ultramarine, cerulean blue (primarily cobalt stanate, and Prussian blue.

Natural dyes to color cloth and tapestries were made from plants. Woad and true indigo were used to produce indigo dye used to color fabrics blue or indigo. Since the 18th century, natural blue dyes have largely been replaced by synthetic dyes.