SED fitting of BSS4 observed photometry (black circles; the same as in Figs. 5 and B.4) through the combination of the SED that best fits the points at λ > 4000 Å (black line, the same as in Fig. B.4) and the SED of different WDs (blue lines): from top-left to bottom-right, a He-WD with a mass of 0.2, 0.3, and 0.4 M_⊙, and a 0.55 M_⊙ CO-WD. The expected fluxes, computed from the convolution of the combined (BSS+WD) best-fit synthetic SED with the adopted photometric filters, are shown as cyan squares, and their error bars and horizontal extension have the same meaning as in the previous figures. The best-fit values of the WD surface temperature and radius are labelled, together with their 1σ uncertainty.