Separation between red and blue galaxies in the MS 1054.4−0321 cluster. Left panel: color−magnitude diagram. The horizontal dashed line indicates the color cut obtained using the V − i colors for member galaxies. For this well-sampled cluster we also show the red sequence line fitted with a two-sigma procedure applied to the red galaxies (black solid line). Larger sizes of the symbols for larger EW[OII] show the good agreement between the photometric and spectroscopic methods to separate red passive from blue star-forming galaxy populations. Right panel: distribution of V − i colors for member galaxies. The two Gaussians are obtained through the KMM method and allow us to define the color cut in the left panel.