Effect of different assumptions of the R_V parameter on the isochrone position in the CMDs. The dashed black line is the 12.5 Gyr isochrone (Bressan et al. 2012) that best fits the NIR CMD (right panel) under the assumption of the (O’Donnell 1994) extinction law with the standard value R_V = 3.1, requiring E(B - V) = 2.08. Clearly, this isochrone is unable to also match the optical CMD (see the dashed black line in the left panel). The solid red line is the same isochrone plotted assuming the same extinction law, but adopting R_V = 2.5: it clearly simultaneously reproduces both the NIR and the optical CMDs well, with E(B - V) = 2.86.