Spectral evolution of QPEs in eRO-QPE3 (left) and eRO-QPE4 (right). The top-right (bottom) subpanels show the luminosity (temperature) evolution with time of the QPE component. Darker to lighter colors represent the evolution from start to end of the eruptions. The first eruptions of the eRO3-XMM1 observation and the second of the eRO4-XMM observation are taken as reference for the QPEs in eRO-QPE3 and eRO-QPE4, respectively. The top-left subpanels show the luminosity-temperature coevolution, analogous to the rate-hardness evolution in Arcodia et al. (2022) which first reported the hysteresis cycle.