Colour distributions of galaxies. Each class is shown in a different row, as noted to the right of the panels. Each column considers a particular range of galaxy stellar mass, as noted at the top. Grey shaded histograms are the real colour distributions, i.e. they correspond to the intrinsic classes. Green lines are the colour distributions of the predicted classes. Violet lines are the colour distributions recovered by our method. We quote within each panel the values of the corresponding square residuals, S^pred and S^rec, given by Eqs. (6) and (7), respectively.