Absolute-K_sGaia-2MASS diagram for the stars with or without a spectral type (top and bottom panels, respectively) in the selected sample. Symbol colors and shapes indicate the spectral type and host cluster described in the legend, respectively, which also reports the number of sources displayed (i.e., having both optical and NIR photometry). The dashed line marks the separation between O- and C-rich sources according to Lebzelter et al. (2018). An arrow marks the source MSX LMC 124 in NGC 1830 that, having W_BP,RP − W_{J,K_s} = 9.73 mag, lies outside the plot area. Background dots are LPVs in the LMC from OGLE-III (light gray) and Mowlavi et al. (2018) (darker gray).