g − r versus r colour-magnitude diagram for member galaxies: red open circles for quenched galaxies, blue open stars for star-forming ones, and grey points for previously confirmed members. The black line represents the best fit for the quenched galaxies that form the red sequence as they all lie along a linear relation (black solid line). This linear relation was fitted in a two-stage process. First we fit a Gaussian function to the g − r colour distribution of the quiescent galaxies (red open circles), deriving its mean and σ. We then apply the Theil-Sen linear regression method (Sen 1968) to all spectroscopic members with g − r colours within 2.5σ of the mean g − r colour of the red sequence (i.e. with g − r > 1.34). We see a bimodal distribution of cluster galaxies, where the quenched galaxies have redder g − r colour compared to the star-forming galaxies.