spectrum (between approximately 380 and 435 nanometers), whereas purple is the color of various combinations of red, blue and violet light, some of which humans perceive as similar to violet. In common usage, both terms are used to refer to a variety of colors between blue and red in hue. Historically, violet has tended to be used for bluer hues and purple for redder hues. In the traditional color wheel used by painters, violet and purple are both placed between red and blue, with violet being closer to blue. In science Optics Violet is at one end of the spectrum of visible light, between blue light, which has a longer wavelength, and ultraviolet light, which has a shorter wavelength and is not visible to humans. Violet encompasses light with a wavelength of approximately 380 to 435 nanometers. Violet objects often appear dark, because human vision is relatively insensitive to those wavelengths. The reason that to (typical trichromat) humans violet light appears a bit reddish compared to spectral blue (despite spectral red being at the other end of the visible spectrum) is because the S-cone type (i.e. the one most sensitive to short wavelengths) contributes a bit of red to the red-versus-green opponent channel (which at the longer blue wavelengths gets counteracted by the M-cone type). Computer and television screens, using the RGB color model, cannot produce actual violet light and instead mimic it with a shade of purple, combining blue light at high intensity with red light at less intensity. Chemistry – pigments and dyes The earliest violet pigments used by humans, found in prehistoric cave paintings, were made from the minerals manganese and hematite. Manganese is still used today by the Aranda people, a group of indigenous Australians, as a traditional pigment for coloring the skin during rituals. It is also used by the Hopi Indians of Arizona to color ritual objects. The most famous violet-purple dye in the ancient world was Tyrian purple, made from a type of sea snail called the murex, found around the Mediterranean. In western Polynesia, residents of the islands made a violet dye similar to Tyrian purple from the sea urchin. In Central America, the inhabitants made a dye from a different sea snail, the purpura, found on the coasts of Costa Rica and Nicaragua. The Mayans used this color to dye fabric for religious ceremonies, and the Aztecs used it for paintings