As in Fig. 2, stellar mass versus colour relations for galaxies in the Virgo (left) and Fornax (right) clusters. The red curve in the panels with g − r illustrates the dividing line for the red fraction, according to Weinmann et al. (2011, to illustrate their linear relation as a function of total magnitude in this figure, the stellar masses were converted to r-band brightnesses using a running mean average relation). The relations are largely consistent for both clusters.