The first definition of primary colour in the dictionary is Also called: additive primary. any of three spectral colours that can be mixed to match any other colour, including white light but excluding black. Other definition of primary colour is Also called: subtractive primary. any one of the spectral colours cyan, magenta, or yellow that can be subtracted from white light to match any other colour. An equal mixture of the three produces a black pigment. Primary colour is also Also called: psychological primary. any one of the colours red, yellow, green, or blue. All other colours look like a mixture of two or more of these colours and they play a unique role in the processing of colour by the visual system.