Probability density distributions of D_n(4000) index (left panel), (g − r)₀ colour index (middle panel), and stellar masses for galaxies (right panel) in groups 2, 5, and 8 (red solid line), groups 3, 4, 6, 7, and 10 − 14 (notation Gr3-14, orange dashed line), in groups 1 and 9 (green dot-dashed line), and in poor groups (blue dotted line). Group ID numbers are given in Table 1.