  The color confinement can be decently explained by assuming the global
$SU(3)$ color symmetry. A hadron is viewed as a bag of a finite size, whose
energy is contributed by the color fields within the hadron. In the large
momentum frame, the mass of a hadron can be quantized and can be expressed as
the sum of the current masses of quarks involved plus a flavor independent term
which depends on a universal parameter and can be identified to be the
contribution from the QCD trace anomaly. This term depicts the Regge's
trajectories of light hadron masses, from which the parameter can be determined
and gives the minimal vector meson mass and baryon mass to be 761 MeV and 935
MeV, respectively. The mass formula can explain many features of the hadron
spectroscopy.
