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Color charge is the gauge group charge of Quantum chromodynamics, associated with its $SU(3)$ symmetry. A quark transforms in the fundamental three-dimensional representation, an antiquark in its conjugate, and a lepton is a singlet. The word color is a label for this charge, unrelated to visible light.

A hadron with integer spin. An ordinary meson has valence content consisting of a quark and an antiquark.

A high-energy hadron is treated as constituents scattering incoherently. In electromagnetic deep inelastic scattering, the charged constituents are quarks and antiquarks.

A constituent quark that does not participate in the elementary weak vertex of a meson decay. It combines with a produced quark or antiquark in the final hadron.