cyan (adjective, colour term; synonym: blue-green) – the hue of the visible light spectrum located between blue and green. The human eye typically perceives monochromatic light with a wavelength somewhere between 475 and 510 nm as cyan. However, a mixture of wavelengths of light can result in the same subjective colour perception. Cyan (C) is one of three subtractive primary colours in the CMY colour model, using the capacity of ink to reflect light to mix different colours. Because of ink impurities, the gamut of colours is fairly limited and a black ink (K) is therefore usually added as a fourth subtractive primary colour (CMYK colour model). In the RBG colour model, which is based on mixing emitted light, cyan is not a primary colour, but generated by mixing blue (B) and green (G) light.