The green flash is a phenomenon that, according to Prunella, supposedly occurs every year at midnight on New Year's Day. In "Arthur's New Year's Eve," she asks Arthur if he's going to stay up to watch this, but he doesn't understand. She realizes that he's never stayed up until midnight on New Year's Eve before, and therefore doesn't know about the green flash. She explains that every year at midnight, people gather to watch the sky for a most amazing green flash. If it happens, it means that the new year has successfully begun. If it does not happen, then it has to stay the same year for another whole year.