  The integrated colors of distant galaxies provide a means for interpreting
the properties of their stellar content. Here, we use rest-frame UV-to-optical
colors to constrain the spectral-energy distributions and stellar populations
of color-selected, B-dropout galaxies at z ~ 4 in the Great Observatories
Origins Deep Survey. We combine the ACS data with ground-based near-infrared
images, which extend the coverage of galaxies at z ~ 4 to the rest-frame
B-band. We observe a color-magnitude trend in the rest-frame m(UV) - B versus B
diagram for the z ~ 4 galaxies that has a fairly well-defined "blue-envelope",
and is strikingly similar to that of color-selected, U-dropout galaxies at z ~
3. We also find that although the co-moving luminosity density at rest-frame UV
wavelengths (1600 Angstroms) is roughly comparable at z ~ 3 and z ~ 4, the
luminosity density at rest-frame optical wavelengths increases by about
one-third from z ~ 4 to z ~ 3. Although the star-formation histories of
individual galaxies may involve complex and stochastic events, the evolution in
the global luminosity density of the UV-bright galaxy population corresponds to
an average star-formation history with a star-formation rate that is constant
or increasing over these redshifts. This suggests that the evolution in the
luminosity density corresponds to an increase in the stellar-mass density of
more than 33%.
