  The variation mechanism of blazars is a long-standing unresolved problem. In
this work, we present a scenario to explain diverse variation phenomena for ON
231, where the jet emissions are composed of the flaring and the less variable
components (most probably from the post-flaring blobs), and the variation is
dominated by shock-in-jet instead of the Doppler effect. We perform correlation
analysis for the multiwavelength light curves and find no significant
correlations. For optical band, ON 231 exhibits a harder when brighter (HWB)
trend, and the trend seems to shift at different periods. Correspondingly, the
correlation between polarization degree and flux exhibits a V-shaped behavior,
and a similar translation relation during different periods is also found.
These phenomena could be understood via the superposition of the flaring
component and slowly varying background component. We also find that the slopes
of HWB trend become smaller at higher flux levels, which indicates the
energy-dependent acceleration processes of the radiative particles. For X-ray,
we discover a trend transition from HWB to softer when brighter (SWB) to HWB.
We consider that the X-ray emission is composed of both the synchrotron tail
and the Synchrotron Self-Compton components, which could be described by two
log-parabolic functions. By varying the peak frequency, we reproduce the
observed trend transition in a quantitative manner. For $\gamma$-ray, we find
the SWB trend, which could be explained naturally if a very-high-energy
$\gamma$-ray background component exists. Our study elucidates the variation
mechanism of intermediate synchrotron-peaked BL Lac objects.
