  We use deep multi-band optical and near-infrared data for four general
fields, GOODS-South, HDF North/South, and IRAC UDF in GOODS-North to
investigate the evolution of the observed rest-frame U-V color of field
galaxies as a function of the stellar mass. In these four fields, the U-V color
distributions of the galaxies at each mass and redshift interval are very
similar. At 0.3<z<2.7, we found that more massive galaxies always tend to have
a redder U-V color. High- and low-mass galaxies exhibit quite different color
evolutions. As seen in our previous study in HDF-N, the color distribution of
low-mass (M_stellar < 3x10^9M_solar) galaxies becomes significantly bluer with
an increase in the redshift. This evolution of the average color can be
explained by a constant star formation rate model with z_form~4. On the other
hand, the average color of high-mass galaxies (M_stellar > 3x10^10M_solar)
evolves more strongly at a high redshift. Such mass-dependent color
distribution and its evolution indicate that galaxies with a larger stellar
mass appear to have shorter star-formation timescales, and on an average, they
form the larger fraction of their stars in the earlier epoch.
