Relations Δcol3–[Na/Fe] for NGC 104, NGC 288, NGC 362, NGC 1851, NGC 2808, and NGC 3201. For each GC, in the left panel the green and magenta symbols mark FG and SG stars, respectively, as classified from HST photometry (through the PCMs). The red triangles represent stars in the so-called red-RGB region. In the right panel, for each GC black circled symbols are stars in common between photometry and spectroscopy, yet they were neglected in Marino et al. Here, FG and SG stars (cyan and red, respectively) are separated according to the spectroscopic Na abundances (see text).