In quantum chromodynamics, quarks come in three color charges.
The labels are conventionally called red, green, and blue. They are abstract quantum charges, not visible colors. Quarks carry one color, while antiquarks carry corresponding anticolors. Gluons carry combinations of color and anticolor and mediate the strong interaction.
Observable particles are color neutral. Baryons contain three quarks whose colors combine to a color singlet, while mesons contain a quark and an antiquark whose color and anticolor cancel. This requirement is part of the explanation for why isolated quarks are not observed under ordinary conditions.
The three-color structure is associated with the SU(3) gauge symmetry of quantum chromodynamics. The number three should not be confused with the eight types of gluon state that arise in the theory. Color charge is also distinct from electric charge, although both are quantum properties carried by elementary particles.