  We derive the fraction of blue galaxies in a sample of clusters at z < 0.11
and the general field at the same redshift. The value of the blue fraction is
observed to depend on the luminosity limit adopted, cluster-centric radius and,
more generally, local galaxy density, but it does not depend on cluster
properties. Changes in the blue fraction are due to variations in the relative
proportions of red and blue galaxies but the star formation rate for these two
galaxy groups remains unchanged. Our results are most consistent with a model
where the star formation rate declines rapidly and the blue galaxies tend to be
dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused
by processes specific to the cluster environment.
