Color characteristics of the blazar S5 0716+714 under geometrical origin of the long-term variability

The optical radiation of the blazar S5 0716+714 is formed within its ultrarelativistic jet in a compact region located near the true origin of the jet. Assuming that the variability is formed only by changing the relativistic radiation amplification coefficient (Doppler factor) for some part of the emitting region and that the spectrum of the emitting region, characterized by a power law at the observed frequencies, has a turn-over at lower frequencies, caused by synchrotron self-absorption, we analyze the archival data of the Crimean Astrophysical Observatory of B-, V-, R-, I-photometry of the blazar S5 0716+714 from 2002 to 2019. An explanation for the observed change in the color index during the blazar S5 0716+714 variability without changes in the physical parameters of the source was obtained.