Top panel: representative 0.2 − 2 keV background-subtracted QPE light curve, centered at the peak and binned to 250 s. Lower panel: hardness ratio (HR) between the 0.6 − 2 keV and the 0.2 − 2 keV count rates as a function of the total count rate, where each point is color-coded following the time evolution of the QPE in the panel above. The HR shows a counter-clockwise evolution, as tracked by the dashed gray arrows. The complete set of HR plots can be found in Fig. B.2.