  We make an exhaustive investigation on the pentaquark states $qqqc\bar{c}$
($q=u, d$ and $s$) and discuss the effect of color structures in a multiquark
color flux-tube model. We exhibit a novel picture of the structure and
properties of the states $P_c$ and $P_{cs}$ observed by the LHCb Collaboration.
We can describe the states as the compact pentaquark states in the model. The
spin-parity of the group of $P_c(4312)^+$ and $P_c(4337)^+$ is $\frac{1}{2}^-$
while that of the group of $P_c(4380)^+$, $P_c(4440)^+$ and $P_c(4457)^+$ is
$\frac{3}{2}^-$. Their structures are pentagon, diquark, pentagon, diquark, and
octet, respectively. The members in each group can be analogically called QCD
isomers because of their the same spin-parity and quark content but different
color structures. The singlet $P_{cs}(4459)^0$ has pentagon structure and
spin-parity of $\frac{1}{2}^-$. In addition, we also predict the $P_{cs}$,
$P_{c ss}$ and $P_{csss}$ families in the model. The five-body confinement
potential based on the color flux-tube picture, which is a collective degree of
freedom and induces QCD isomer phenomenon, plays an important role in the
formation of the compact states.
