We discuss the environmental dependence of galaxy colors at z<1.3 and show that galaxies follow the "environment-dependent down-sizing" evolution. We suggest that galaxy-galaxy interactions may be the primary driver of this evolution. Red galaxies in groups at z~0.8 and in the field z~0.5 show strong Hd absorptions for their colors. Interestingly, these are the environments in which we observe the on-going build-up of the red sequence. The strong Hd absorptions imply that their star formation rates decreased on a relatively short time scale (<1Gyr). We suggest that galaxy-galaxy interactions are likely the driving process of the truncation of the star formation activities and the build-up of the red sequence.