Wanda's hair was originally planned to be blue, but her hair was changed to pink so it would not clash with Timmy's bedroom walls.
Timmy's pink hat was originally going to be blue, but Butch Hartman's blue marker ran out of ink while designing the character, so he randomly grabbed a pink marker to color it in instead. The in-universe explanation given on the show to Timmy's pink hat is that Timmy's parents were expecting to have a daughter so they bought all pink clothes, including one pink hat.
The Tooth Fairy's costume and equipment are based on those of Wonder Woman.