Color − magnitude diagram using Yonsei-Yale isochrones for 1 Gyr (dashed lines), 5 Gyr (dotted lines), and 12 Gyr (full lines), and metallicities [Fe/H]  =  −3.6 (lowest value possible within the Yonsei-Yale set in black), [Fe/H]  =  −3.0 (gray), [Fe/H]  =  −2.0 (red), [Fe/H]  =  −1.0 (blue), [Fe/H]  = 0.0 (green). [α/Fe] is set to +0.4 for all isochrones except for [Fe/H]  = 0.0, which have [α/Fe]  = 0.0 and an extra set of isochrones plotted for [Fe/H]  =  −1 and [α/Fe]  = 0.0 (cyan). The vertical line roughly indicates the onset of the RGB.