  We report the first results of a long term program aimed at investigating the
photometric properties of the cores of Abell and X-ray selected (EMSS,
\cite{emss}) clusters of galaxies. We observed 77 clusters of galaxies in the
redshift range $0.05\leq z \leq 0.25$ in the Gunn $g$, $r$ and $i$ filters: in
this paper we present the data on 59 clusters with good absolute photometry and
on another group of 8 clusters with acceptable relative photometry. For all
these clusters we show color--magnitude diagrams in the two colors: when, as in
most cases, the early type galaxy sequence is identifiable, we compare it with
the expectation from the Virgo c--m relation (\cite{vs}) and find that the
Virgo relation holds to $z\sim0.2$. We do not find any sign of active evolution
in cluster galaxies since that epoch, nor in the percentage of blue galaxies or
in the early type galaxy colors, if we accept that the scatter is of the order
of 0.2--0.3 mag with respect to the expectations on the basis of standard
k--corrections. We point out the presence of a certain number of anomalously
red galaxies in the $r-i$ color, which are too red with respect to their $g-r$
color to be normal field galaxies at a redshift higher than the cluster one.
Finally we briefly compare a few properties of the two subsamples of optically
selected and X--ray selected clusters.
