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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Source. Some decent visualizations of how the field lines don't expand out like they do in electromagnetism, suggesting color confinement.PHYS 485 Lecture 6: Feynman Diagrams by Roger Moore (2016)
Source. Despite the title, this is mostly about QCD.