UKIDSS-2MASS K_s versus J − K_s diagrams of regions REG2 (top-right), REG4 (top-left), REG5 (middle-left), REG7 (middle-right), RSGCX1 (bottom-left) from Table 1. 2MASS data are used for K_s brighter than 10.5 mag. Spectroscopically observed stars are labeled as summarized in the legend. Of stars are marked with asterisks, late-O and early-B types with circles, late-B and early-A stars with squares. Possible foreground early-types (A_Ks< 0.8 mag) are marked with crosses. Triangles indicate RSGs/cRSGs. The bottom-right panel shows a map (WISE 3.4 μm) of RSGCX1, where squares indicate the observed giants, and triangles the cRSGs.