(A) Specular reflectance spectra of a 200 ML ethane film atop a 1000 ML water ice at 55 K, recorded over time during 3.5 hours (210 minutes) of annealing. The image displays minimal spectral change. (B, C) QCM images of the ethane–water ice layer at 55 K at 0 and 210 minutes, respectively. These images show no visible color transition. (D) Time-series reflectance spectra at 60 K showing pronounced reddening within 3.5 hours. (E, F) Corresponding QCM images at 60 K at 0 and 210 minutes, respectively. These images clearly illustrate the thermal reddening of the ethane-coated ice.