Left: colour–magnitude diagram with the corresponding red sequence indicated by a solid line and its 3σ = 0.249 magnitude intervals by dashed lines. The sample is complete down to the curve at  ~22 mag, which varies slightly with the B − R colour. We thus limited the analysis to the galaxies brighter than R = 22 mag. The dotted line denotes the colour cut that is 1.5 mag bluer than the red sequence, below which the objects were considered as foreground contamination. Red stars and blue diamonds indicate red and blue spectroscopic member galaxies regardless of their clustercentric distances. The BCG is extremely blue with B − R = 0.98. Right: cluster galaxy luminosity functions for red (red stars), blue (blue diamonds), and all (black circles) members within derived from the X-ray hydrostatic mass estimate. The membership is statistically determined using control fields with the background contamination statistically subtracted. The best-fit Schechter (1976) functions are shown in red and black curves for the red and all members, respectively. The inset shows the 68% confidence region for the R ^⋆  and α parameters of the best-fit Schechter (1976) functions. No fit was possible for the blue members.