LCOGT light curves of ExtEV in Johnson U (purple dots), B (blue dots), and V (green dots) passbands. Panel a shows the light curves. A ±0.25 mag vertical offset was applied to U and V-filter light curves to avoid overlapping. Panels b–d show the light curves phased with the orbital period. Phase zero corresponds to the time of periastron passage. In addition, we have drawn dash-dotted lines in each of the lower panels to indicate the range of variability during the heartbeat. The plot illustrates that the range is virtually the same in all three passbands.