J−K data plotted against V−K data for the red supergiants in the four clusters: open circles, red supergiants of NGC 330; filled circles, NGC 1818; squares, NGC 2004; crosses, NGC 2100. Colors have been dereddened (see text for details). Error bars are approximate. The dotted line shows the predicted locus for log  g = +0.5 and [Fe/H﹩] =-0.60﹩ (Plez et al. 1997).