About

The charge of QCD is called "color" and comes in three fundamental values called "red", "green", and "blue", to which are coupled eight distinct states of a single vector boson called a "gluon".

Unlike the photon in QED, gluons are themselves color charged objects, which means the theory is complicated by the existence of three- and four-gluon vertexes.

A important feature of the strong interaction is confinement, which demands that all all objects able to exist at large distance separation must be color-neutral: either adding equal amounts of red, green, and blue (as in baryons); or by adding color and anti-color (as in mesons).

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