This reminds me of a machine vision application for large-scale bakeries. When you bake bread, the color of the surface changes as the bread rises and completes

This reminds me of a machine vision application for large-scale bakeries. When you bake bread, the color of the surface changes as the bread rises and completes the baking process. In the application I remember, the average color of a loaf was tracked on an RBG plot as a function of time. The idea was that the baking process followed a trajectory in the RGB space that was dependent on the temperature of the oven and the elapsed time. This can be used as feedback for process control-- to signal when to pull out the bread or to change the temperature. In a similar way the color of paintings change as they age. The individual points in the OP's plots could be parameterized in time and according to paint's chemistry. It might be possible, after some calibration studies, to accurately simulate aging. Or better, simulate the reversal of aging to show what an old aged painting looked like when it was new.