Colour dependence of the halo mass. Blue histogram: marginal posterior probability distribution of the parameter ν_h, describing the dependence of the average halo mass as a function of excess colour at a fixed redshift, stellar mass, and size, as defined in Eq. (35). Pink histogram: marginal posterior probability distribution of the parameter ν_h, describing the dependence of the average halo mass as a function of excess colour at a fixed luminosity and size, as inferred in Sect. 4.