Woad in the context of "Lincoln green"

Blue is one of the three primary colours in the RGB (additive) colour model, as well as in the RYB colour model (traditional colour theory). It lies between violet and cyan on the spectrum of visible light. The term blue generally describes colours perceived by humans observing light with a dominant wavelength between approximately 450 and 495 nanometres. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called the Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called aerial perspective.

Blue has been an important colour in art and decoration since ancient times. The semi-precious stone lapis lazuli was used in ancient Egypt for jewellery and ornament and later, in the Renaissance, to make the pigment ultramarine, the most expensive of all pigments. In the eighth century Chinese artists used cobalt blue to colour fine blue and white porcelain. In the Middle Ages, European artists used it in the windows of cathedrals. Europeans wore clothing coloured with the vegetable dye woad until it was replaced by the finer indigo from America. In the 19th century, synthetic blue dyes and pigments gradually replaced organic dyes and mineral pigments. Dark blue became a common colour for military uniforms and later, in the late 20th century, for business suits. Because blue has commonly been associated with harmony, it was chosen as the colour of the flags of the United Nations and the European Union.

The Unicorn Tapestries or the Hunt of the Unicorn (French: La Chasse à la licorne) is a series of seven tapestries made in the Southern Netherlands around 1495–1505, and now in The Cloisters in New York City. They were possibly designed in Paris and woven in Brussels. They depict a group of noblemen and hunters in pursuit of a unicorn through an idealised French landscape. The tapestries were woven in wool, metallic threads, and silk. The vibrant colours, still evident today, were produced from dye plants: weld (yellow), madder (red), and woad (blue).

First recorded in 1680 in the Paris home of the Rochefoucauld family, the tapestries were looted during the French Revolution. Rediscovered in a barn in the 1850s, they were hung at the family's Château de Verteuil. Since then they have been the subject of intense scholarly debate about the meaning of their iconography, the identity of the artists who designed them, and the sequence in which they were meant to be hung. Although various theories have been put forward, currently nothing is known of their early history or provenance. Their dramatic but conflicting narratives have inspired multiple readings, from chivalric to Christological. Variations in size, style, and composition suggest they come from more than one set, linked by their subject matter, provenance, and the mysterious AE monogram which appears in each. One of the panels, "The Mystic Capture of the Unicorn", survives as just two fragments.