  We analyse the B-R_c colors of galaxies as functions of luminosity and local
galaxy density using a large photometric redshift catalog based on the
Red-Sequence Cluster Survey. We select two samples of galaxies with a magnitude
limit of M_Rc<-18.5 and redshift ranges of 0.2<z< 0.4 and 0.4<z<0.6 containing
\~10^5 galaxies each. We model the color distributions of subsamples of
galaxies and derive the red galaxy fraction and peak colors of red and blue
galaxies as functions of galaxy luminosity and environment. The evolution of
these relationships over the redshift range of z~0.5 to z~0.05 is analysed in
combination with published results from the Sloan Digital Sky Survey. We find
that there is a strong evolution in the restframe peak color of bright blue
galaxies in that they become redder with decreasing redshift, while the colors
of faint blue galaxies remain approximately constant. This effect supports the
``downsizing'' scenario of star formation in galaxies. While the general
dependence of the galaxy color distributions on the environment is small, we
find that the change of red galaxy fraction with epoch is a function of the
local galaxy density, suggesting that the downsizing effect may operate with
different timescales in regions of different galaxy densities.
