Illustration of the Gaussian process inference described in Section 2.3 as applied to the light curve of 2019gvw. First panel: SALT2 fit to the light curve, along with observations (binned to 1 day resolution). Second panel: residuals of SALT2 fit. These residuals show both correlated behavior and uncorrelated noise. Third panel: Gaussian process, conditioned on observed residuals, with hyperparameters from Table 1, showing the possible correlated structure we ultimately hope to include in the trained SALT model. Fourth panel: leave-one-out residuals from Gaussian process, showing expected scatter and reduced correlation.