CMDs with color coded MIR variability. Upper left panel: WISE4 magnitude versus K_S –WISE3 color. The MIR variability is evident(median_MADWISE1 ≈ 0.048 mag) for targets with K_S–WISE3 ≥ 1.0 mag and WISE4 ≤ 6.5 mag, while targets with K_S –WISE3 ≤ 1.0 mag andWISE4 ≥ 6.5 mag exhibit much smaller MIR variability (median_MADWISE1 ≈ 0.007 mag). Upper right panel: WISE4 flux versus MLR. TheWISE4 (22 µm) flux grows exponentially along with the increasing of the volume or brightness of the star. Since the variability and luminosityare degenerate, both of them may have important contribution to the MLR. Lower panels: WISE1/J–WISE1 and IRAC1/J–IRAC1 diagrams. A turning point around IRAC1 ≈ 8.7 mag is shown by the dashed line in IRAC1/J–IRAC1 diagram separates well two populations (brighter and fainter) of RSGs with different MIR variability.