PanSTARRS magnitude diagrams: r − i vs. r (upper panel) and g − r vs. r (lower panel) of member galaxies of A1213 (green points) and the background eastern group (red squares, see Sect. 5). Large green squares show the BCG and the pair of bright galaxies: BG1 and BG2. Black lines show the color-magnitude relations obtained for the A1213 member galaxies. The blue dashed line in the lower panel is used to separate red galaxies from blue ones.