QCD is the fundamental theory to describe the strong interaction, where quarks and gluons have the color degrees of freedom. However, a single quark or gluon can not be separated out and all observable particles are color singlet states. Color confinement or quark confinement conjecture can be proved by considering not only the strong interaction but also the electroweak interaction which is $SU(3)_c$ invariant. Any measurable state has to be color singlet is the direct consequence of the common symmetry of the standard model. Color non-singlet objects are created from the big bang when the interaction breaks $SU(3)_c$ symmetry based on the nonlocal Lagrangian. There is nearly no interaction between colored objects and color singlet universe when the momentum transfer is not large enough. Colored objects are reasonable candidates of dark matter and the missing of anti-matter in the universe can also be easily explained. Dark matter can be produced in the laboratory which can be tested by measuring the energy loss and baryon number change in the extremely high energy collisions of particles and anti-particles.
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