Color–color diagrams of z − H vs. r − z (upper) and z − K vs. r − z (bottom). Upper left panel: examples of KDE (contours) and MAD (solid circles indicate the median values of z − H color in equal bins (from 0.3 to 2.6 with a step of 0.2 mag) of the r − z color, and the error bars indicate three times of MAD for the corresponding bin), both of which fail to include all the spectroscopically confirmed RSGs. Left panels: original data without the overlapping MARCS models, right panels: MARCS-model selected LSG region (dashed lines are hand-drawn). Small and large solid circles and diamonds represent HSG and LSG targets at different T_eff (from 3300 to 4250 K) in different metallicities derived from MARCS models, respectively. Spectroscopically confirmed RSGs from Levesque & Massey (2012) and Patrick et al. (2015) are shown as open pentagon and solid stars, respectively. A reddening vector of A_V = 1.0 mag is shown as a reference (same below). The error bars in the bottom right corner of the right panels indicate the median error of each color.