Quantum Chromodynamics (QCD) is the theory that describes the strong interaction, one of the four fundamental forces in nature, which governs the behavior of quarks and gluons—the fundamental particles that make up protons, neutrons, and other hadrons.
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Quantum chromodynamics is the gauge theory of quarks and gluons. At low energies it confines coloured fields into gauge-singlet hadrons.
Quarks, Gluon flux tubes, Strong Nuclear Force, & Quantum Chromodynamics by Physics Videos by Eugene Khutoryansky (2018)
Source. Some decent visualizations of how the field lines don't expand out like they do in electromagnetism, suggesting color confinement.