I'm going to say it's a strong Teen rating for swears.

Gen 0 - Purple
Part 1 - Purple as Heck
Gen 1 - Blue
Part 2 - Pervy Gnomes and Questionable Baby Names
Part 3 - Gender Issues, Prom Drama, and Too Many Birthdays
Part 4 - The Mysterious IF, Crystal Meth in Egypt, and Death
Takes Out the Trash
Gen 2 - Green
Part 5 - Attack of the Gnomes