Blue (color)

Blue—also called buluug, cirdhow, or cirtuu in Somali—is one of the primary colors that the human eye can distinguish. It arises from light with short wavelengths compared to red and green. The Somali name directly relates to the word 'cir' (sky), since the sky in ordinary daylight appears this color.

Blue is one of the three primary colors in the RGB (red-green-blue) system used in phone and computer displays. In the CMYK printing system, an equivalent color called cyan is used. Blue therefore plays a role in image and screen technology.

Why the sky is blue

Sunlight contains many colors. When it enters Earth's atmosphere, small particles in the air scatter the light; scattering is stronger for light with shorter wavelengths—which is blue. For this reason, when we look at the sky, we receive more blue light. This process is called Rayleigh scattering. For the same reason, when the sun rises or sets, light travels through a longer path of atmosphere, blue light is scattered away, and red and orange light remains.

Historical use of blue dyes

The most well-known blue dye historically is indigo, extracted from plants grown especially in India and Africa. The indigo trade was an important ocean commerce for centuries. Lapis lazuli, a stone quarried in Afghanistan, yielded an expensive blue dye used for religious paintings. In the nineteenth century, synthetic dye production began on an industrial scale, which widened its use.

Social and cultural meaning

Blue is associated in many cultures with the sea, sky, stability, and trust. It appears in the flags of many countries and is used as the emblem of several international organizations. The work clothes and everyday garments that became standard in the twentieth century were based on indigo dye.