  Blazars are a kind of active galactic nuclei (AGN) in which a relativistic
jet is considered to be directed along the line of sight. They are
characterized by strong and rapid variability of the flux and high
polarization. We performed a monitoring of 41 blazars in the optical and
near-infrared regions from 2008 to 2009 using TRISPEC attached to the "Kanata"
1.5-m telescope. In this paper, we report the correlation of the flux, color
and polarization using our data, and discuss universal features for blazars,
which have not fully been established. Three blazars (3C 454.3, QSO 0454$-$234,
and PKS 1510$-$089) tended to be redder when they were brighter, only during
their faint states. This color behavior suggests that the contribution of a
thermal component is strong in the faint states for those objects. Excluding
this "redder-when-brighter" phase, we found that 24 blazars tended to be bluer
when they were brighter. This number corresponds to 83% among well-observed
objects which we observed for $>10$ nights. Thus, we conclude that the
"bluer-when-brighter" trend is a universal feature for blazars. On the other
hand, the correlation of the flux and the polarization degree is relatively
weak; only 10 objects showed a significant positive correlation. We also
investigated the luminosity-dependence of the color and polarization, and found
that lower luminosity objects have smaller variation amplitudes both in the
flux, color, and polarization degree.
