  We report on a recent multi-band optical photometric and polarimetric
observational campaign of the blazar OJ 287 which was carried out during
September 2016 -- December 2017. We employed nine telescopes in Bulgaria,
China, Georgia, Japan, Serbia, Spain and the United States. We collected over
1800 photometric image frames in BVRI bands and over 100 polarimetric
measurements over ~175 nights. In 11 nights with many quasi-simultaneous
multi-band (V, R, I) observations, we did not detect any genuine intraday
variability in flux or color. On longer timescales, multiple flaring events
were seen. Large changes in color with respect to time and in a
color--magnitude diagram were seen, and while only a weak systematic
variability trend was noticed in color with respect to time, the
color--magnitude diagram shows a bluer-when-brighter trend. Large changes in
the degree of polarization, and substantial swings in the polarization angle
were detected. The fractional Stokes parameters of the polarization showed a
systematic trend with time in the beginning of these observations, followed by
chaotic changes and then an apparently systematic variation at the end. These
polarization changes coincide with the detection and duration of the source at
very high energies as seen by VERITAS. The spectral index shows a systematic
variation with time and V-band magnitude. We briefly discuss possible physical
mechanisms that could explain the observed flux, color, polarization, and
spectral variability.
