  We show how the observed bimodality in the color distribution of galaxies can
be explained in the framework of the hierarchical clustering picture in terms
of the interplay between the properties of the merging histories and the
feedback/star-formation processes in the progenitors of local galaxies. Using a
semi-analytic model of hierarchical galaxy formation, we compute the color
distributions of galaxies with different luminosities and compare them with the
observations. Our fiducial model matches the fundamental properties of the
observed distributions, namely: 1) the distribution of objects brighter than
M_r = -18 is clearly bimodal, with a fraction of red objects increasing with
luminosity; 2) for objects brighter than M_r = -21 the color distribution is
dominated by red objects with color u-r = 2.2-2.4; 3) the spread on the
distribution of the red population is smaller than that of the blue population;
4) the fraction of red galaxies is larger in denser environments, even for
low-luminosity objects; 5) the bimodality in the distribution persists up to z
= 1.5. We discuss the role of the different physical processes included in the
model in producing the above results.
