Evidence for MAPbI3 perovskite film color serving as an indicator of perovskite solar cell degradation was directly established in Hashmi et al. . Evidence for correlation between the color and efficiency change is shown in Figure , with color change of the solar cells in Hashmi et al. shown as a function of their efficiency. Efficiency values in Figure are linearly interpolated due to the different time points of measuring efficiencies and colors, see Supplementary Section S1). Color works as a proxy here, because one of the perovskite decomposition products, PbI2, has a much larger bandgap (2.27 eV ) than the original film, MAPbI3 (1.52 eV ). This results in the yellowing of lead iodide perovskites under environmental stress. The utility of the color proxy as a means to identify more stable perovskite compositions was demonstrated in a study by Sun, Tiihonen et al. as shown in Figure : Proxy measurements on bare films within the MA-FA-Cs lead iodide quasi ternary phase diagramimplemented using the first generation degradation chamber shown in Figure indicated a more stable composition centered at Cs0.17MA0.03FA0.80PbI3; it was 3x more stable than the reference state-of-the-art Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 and yielded in 30% less degradation in a damp heat test when tested directly at the device level. A correlation between color and degradation is established within the limits of the decomposition products remaining optically distinguishable from the original phase within the wavelengths defined by the equipment. Optical cameras with Red, Green, and Blue channels (approx. 550-700 nm, 450-650 nm, and 400-550 nm, respectively, for commercial cameras but highly dependent on the camera model ) have reduced sensitivity for colors outside their spectral sensitivity area, i.e., approximately below 1.78 eV. The spectral sensitivity range of commercial cameras can be extended to up to approximately 900 nm (1.4 eV) by the removal of an integrated infrared filter from the camera. The spectral sensitivity of each setup should be measured because the camera lens and other components absorbing irradiation affect the result. For example, the mixed MA-FA-Cs lead iodide perovskites investigated in Sun, Tiihonen et al. have a potential degradation route via dark minority-phase formation (e.g., perovskite-structured CsPbI3 suggested with computationally estimated bandgap of 1.57 eV ) in addition to decomposition of perovskite into yellow by-products. Thus, the infrared filter was removed from the camera in the first generation MIT chamber (Figure ) to better avoid these dark-coloured "false positives".