blue (adjective, colour term) – the hue of the visible light spectrum located between green and magenta. The human eye typically perceives monochromatic light with a wavelength somewhere between 400 and 510 nm as blue. However, a mixture of wavelengths of light can result in the same subjective colour perception. Blue (B) is one of three additive primary colours in the RGB colour model, using emitted monochromatic light to generate all different colours. For the subtractive colour model, blue colour is not used as a primary colour but generated by mixing inks of the two subtractive primary colours cyan (C) and magenta (M).