TV-Y7 was the most common rating for Greeny Phatom, used in almost every episode (an exception is for the Pilot, as that episode is rated TV-Y7-FV). Starting from season 20, the series is now rated TV-PG.
Meaning of TV-Y7
In real life programs rated TV-Y7 are designed for children age 7 and older. The FCC implies that it "may be more appropriate for children who have acquired the developmental skills needed to distinguish between make-believe and reality." The thematic elements portrayed in programs with this rating may include 'comedic violence', or may be frightening or confusing for children under the age of 7.
Programs given the "FV" content descriptor exhibit more 'fantasy violence', and are generally more intense or combative than other programs rated TV-Y7.