A quality of light, depending on its wavelength. Spectral colour of an emission of light is its place in the rainbow spectrum. Perceived colour (or visual colour) is the quality of light emission as conveyed by the human eye, combining the impressions of 3 types of light-sensitive cells which the eye contains. Perceived colour can be the response to certain combinations of spectral colours, e.g. brown responds to green and red (or blue, yellow and red).