1) Watch the episode of Rugrats called "Waiter, There's a Baby in my Soup"

2) Notice the scene at the beginning where Didi is going over the phone numbers.

3) The first time you see her she has a purple towel on her head.

4) Then the camera goes over to some one else and when they come back to Didi, the towel is red.

5) Then they show Grandpa going somewhere and after that they go back to Didi and the towel is purple again.