We present the results of our optical ( VRI ) observations of the TeV blazar PG 1553 + 113 over eight nights in 2016 April .
We monitored the blazar quasi-simultaneously in V and R bands each night and examined the light curves ( LCs ) for intraday flux and color variations using two of the most powerful tests ; the power-enhanced F -test and the nested ANOVA test .
The source was found to be significantly ( > 99 \% ) variable in both V and R bands only on April 13 , while clear variations only in R band LCs were seen on April 8 and 12 .
No temporal variation was seen in the color during the observation period .
We did not find any significant correlation between V-R color index and R magnitude on any observing night .
We found a mean optical spectral index of \sim 0.83 \pm 0.02 with a maximum variation of 0.21 by fitting a power law ( F _ { \nu } \propto \nu ^ { - \alpha } ) in the optical ( VRI ) spectral energy distribution of PG 1553 + 113 .
We briefly discuss the possible physical processes responsible for the observed flux and spectral variability .