Note that the word ‘colour’ here is not to be taken in any way literally. The reason three types of colour charge were needed, rather than just two (as with electric charge), was to explain why protons and neutrons must each contain three quarks; and the reason the analogy with colour was chosen was because of the connection with the way the three different colours of light (red, blue and green) combine to produce white light. Thus, the three quarks in a proton or a neutron each carry a different colour charge: red, blue or green, which combine to produce a particle that has to be
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