Thomas has a fair few of those type of things hun, same with the door thing and certain teddies have to be in certain places etc.
When I was potty training him he would only wear postman pat pants!
wasn't too bad because he had 5 pairs but then he refused to wear the yellow ones and the red ones so 3 pairs
. Can you get a purple clothes dye and dye all her pants the same colour make life a little easier for now. You will probably find that once she gets completely comfortable with the whole process she will be more relaxed about what she wears etc.
Sounds like it wont take her long hun - good luck!
xx