Log cabin quilts were used in the underground railroad as a message, when the centers of the log cabin were black, it meant this house was a safe house. you could get help there, I find this very interesting. There were many different quilts that were used to signal to the weary travelers, isn't that a creative bunch of people, who would suspect a quilt airing out on your fence or tree.
But to answer your question, traditionally it was yellow or red. But scrappy is scrappy, I have used every color as the center stone, except black. But, if someone needs saving, come on in. LOL