Three color clusters were identified among the samples by feeding the time-series optical data (concatenated time-series of the red, green, and blue pixel values of each sample) into the hierarchical clustering algorithm (Supplementary Figure , detailed description of the approach in the Experimental). These three color clusters were then overlaid atop the quasi-ternary composition diagram, as shown in Figure . The mean RGB color data (Figure ) shows the differing degradation fingerprints among the clusters. In RGB representation, yellowing of the perovskites (due to perovskite decomposition into PbI2) is seen as the blue color decreasing relative to the green and red colors. Cluster 0 shows yellowing throughout the aging test, cluster 1 retains color relatively well, and cluster 2 samples retain color after the changes seen in the first minutes of the aging test, yet the stabilized color is yellow.