Change color of civilizations

In what file can I change the color of civilizations? I want to play Germany for example but I really dont like the white and black or white and grey color. I would like something like red and white like austria has. Where can i change it? what file? thanks.

You have to edit:

CIV5Colors.xml and CIV5PlayerColors.xml

(CIV5Colors_Expansion.xml and CIV5PlayerColors_Expansion.xml for expansion civs)

Thanks for the reply, worked

Could we get a step by step instruction? I'd like to trade the colors of Rome and Persia.