(U − B) colour and the blue fraction of galaxies (f_{blue,centrals}) and their environment (f_{blue,environment}) in different stellar mass bins: (U − B) and f_blue as a function of nearest-neighbour density log (1 +δ₃) for galaxies in four stellar mass bins. From top to bottom: (U − B) of galaxies, mean (U − B) of the galaxies' neighbours, f_blue of galaxies, f_blue of neighbours. The stellar mass bins are colour coded and plotted with different symbols: blue triangles (log M_* < 10.5), cyan squares (10.5 < log M_* < 11), green stars (11 < log M_* < 11.5) and red circles (log M_* > 11.5). The error bars represent the 3σ error of the mean in each bin.