  In an optical monitoring program to characterize the variability properties
of blazar, we observed 10 sources from the Roma-BZCAT catalogue for 26 nights
in V and R bands during October 2014 to June 2015 with two telescopes located
in India. The sample includes mainly newly discovered BL Lacs where the
redshift of some sources are not known yet. We present the results of flux and
color variations of the sample on intraday and short time scales obtained by
using the power-enhanced F-test and the nested-ANOVA tests, along with their
spectral behavior. We find significant intraday variability in the single FSRQ
in our sample, having an amplitude of variation ~12%. Although a few of BL Lacs
showed probable variation in some nights, none of them passes the variability
tests at 99.9% significance level. We find that 78% of the sample showed
significant negative colour--magnitude correlations i.e., a
redder-when-brighter spectral evolution. Those which do not show strong or
clear chromatism, predominantly exhibit a redder-when-brighter trends. Unlike
on hourly timescales, the high synchrotron peaked (HSP) blazars in the sample
(BZGJ0656+4237, BZGJ0152+0147 and BZBJ1728+5013) show strong flux variation on
days to months timescales, where again we detect a decreasing trend of the
spectral slope with brightness. We observe a global steepening of the optical
spectrum with increasing flux on intranight timescale for the entire blazar
sample. Non-variability in the BL Lacs in our sample could be resulted by
distinct contribution from the disk as well as from other components in the
studied energy range.
