  We have monitored the BL Lac object Mrk 501 in optical $V$, $R$ and $I$ bands
from 2010 to 2015. For Mrk 501, the presence of strong host galaxy component
can affect the results of photometry. After subtracting the host galaxy
contributions, the source shows intraday and long-term variabilities for
optical flux and color indices. The average variability amplitudes of $V$, $R$
and $I$ bands are $22.05\%, 22.25\%, 23.82\%$ respectively, and the value of
duty cycle 14.87 per cent. A minimal variability timescale of 106 minutes is
detected. No significant time lag between $V$ and $I$ bands is found on one
night. The bluer-when-brighter (BWB) trend is dominant for Mrk 501 on
intermediate, short and intraday timescales which supports the shock-in-jet
model. For the long timescale, Mrk 501 in different state can have different
BWB trend. The corresponding results of non-correcting host galaxy
contributions are also presented.
