  We report on simultaneous $g'$, $R_{\rm c}$ and $I_{\rm c}$ photometry of SU
Ursae Majoris during 2011 December - 2012 February using OAO/MITSuME. Our
photometry revealed that quiescence is divided into three types based on the
magnitude and color. Quiescent light curves showed complicated profiles with
various amplitudes and time scales. Although no superoutbursts were observed
during our run, five normal outbursts occurred with intervals of 11 - 21 d. The
shapes of the normal outbursts were characteristic of the outside-in type.
During the rising phase of a normal outburst, the light curve showed periodic
modulations with a period of ${\sim}$ 0.048111(354) d, but the origin of this
peirod was unclear. We examined daily averaged color-color diagram and found
that two cycles exist. This implies that the thermal limit cycle in SU UMa is
complicated. We newly discovered that $g'-R_{\rm c}$ becomes red about 3 days
prior to an outburst. Although the working mechanism on this reddening is
unclear, we propose two possibilities: one is that the inner portion of the
accretion disk is filled by matter and obscures the central white dwarf, and
the other is that the stagnation effect works in the outer region of the
accretion disk.
