  We monitored BL Lacertae frequently during 2014 - 2016 when it was generally
in a high state. We searched for intra-day variability for 43 nights using
quasi-simultaneous measurements in the B, V, R, and I bands (totaling 143 light
curves); the typical sampling interval was about eight minutes. On hour-like
timescales, BL Lac exhibited significant variations during 13 nights in various
optical bands. Significant spectral variations are seen during most of these
nights such that the optical spectrum becomes bluer when brighter. The
amplitude of variability is usually greater for longer observations but is
lower when BL Lac is brighter. No evidence for periodicities or characteristic
variability time-scales in the light curves was found. The color variations are
mildly chromatic on long timescales.
