Go to the episode where Martha's oldest friend (I think her name is Mindy) and go to the bit at the end when she is talking to George and Martha while sitting in the car, and then she drives off. Watch her wig: when the camera is showing her side, Mindy has a reddish wig on. then the view suddenly goes behind her when she starts the car. amazingly, her wig is suddenly jet black!

-Maybe hippo wigs are magic and can change color and shape?