blue - choose a jigsaw puzzle to solve

Blue is one of the three primary color of pigments in painting and traditional color theory , as well as in the RGB color model. It lies between violet and green on the spectrum of visible light . The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495 nanometres. Most blues contain a slight mixture of other colors ; azure contains some green , while ultramarine contains some violet . The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called Tyndall scattering explains blue eyes . Distant objects appear more blue because of another optical effect called atmospheric perspective. Blue has been an important color 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 color fine blue and white porcelain .