Intra-day optical multi-band quasi-simultaneous observation of BL
  Lacertae object S5 0716+714 from 2013 to 2016
  We perform quasi-simultaneous optical multi-band monitoring of BL Lac object
S5 0716+714 on seven nights from 2013 to 2016. Intra-day variability (IDV) is
found on all seven nights. The source was faintest on JD 2456322 with 14.15
mags and brightest on JD 2457437 with 12.51 mags in the $R$ band. The maximum
intra-day variation we observed is 0.15 mags in the $B$ band on JD 2456322.
Both bluer-when-brighter and achromatic spectral behaviours were observed on
the intra-day timescale. On the longer-term scale, the object exhibited a mild
bluer-when-brighter behaviour between the $B$ and $R$ bands. We estimate the
inter-band lags using two independent methods. The variation in the $B$ band
was observed to lag that in the $I$ band by about 15 minutes on JD 2457315. We
compare this lag with one reported previously and discussed the origin of these
lags.
