Colour–magnitude diagram r′ − z′ vs. z′ (right) and the r′ − z′ colour distribution (left) of the cluster members. Open circles show the cluster members sample and filled circles are the FIR-emitter cluster sample. Blue circles are spectroscopic sources, and black circles are photometric cluster candidates. The red curves show the best-fit Gaussian functions and the dot-dashed black line indicates the boundary between optical red and blue galaxies.