Color–magnitude relations for NGC 6034 (top), 1RXS J235814.4+150524 (middle), and RX J1119.7+2126 (bottom). Dots: all galaxies detected along the lines of sight. Filled circles: galaxies spectrocopically classified as group members. Open circles: galaxies that potentially are members of the group from their photometric redshift. The blue crosses (middle and lower figures) are potential group members (from photometric or spectroscopic redshifts) less than two magnitudes fainter than the dominant group galaxy but which are more distant than half the virial radius from the group center. They are therefore no indrance to classify the group as a fossil structure. The red lines are the mean red sequences computed selecting spectroscopic group members and potential members through photometric redshifts.