  The Abelian decomposition of QCD which decomposes the gluons to the color
neutral binding gluons (the neurons) and the colored valence gluons (the
chromons) gauge independently naturally generalizes the quark model to the
quark and chromon model which could play the central role in hadron
spectroscopy. We discuss the color reflection symmetry, the fundamental
symmetry of the quark and chromon model, and explain how it describes the
glueballs and the glueball-quarkonium mixing in QCD. We present the numerical
analysis of glueball-quarkonium mixing in $0^{++}$, $2^{++}$, and $0^{-+}$
sectors below 2 GeV, and show that in the $0^{++}$ sector $f_0(500)$ and
$f_0(1500)$, in the $2^{++}$ sector $f_2(1950)$, and in the $0^{-+}$ sector
$\eta(1405)$ and $\eta(1475)$ could be identified as predominantly the glueball
states. We discuss the physical implications of our result.
