I didn't know that ANY brake fluid came in different colors, but it is unnecessary. Simply start flushing (bleeding) and watch for the fluid to start coming out clear before moving to the next wheel. For a really good flush, go back to each wheel again after you have gotten clear fluid from all of them in give it another good squirt or two.

I would do that car with DOT3 which is much better than what they had in those days anyway.

BTW When I was in elementary school in the fifties a neighbor friend of mine had a '56 Imperial. What a car for its day!

Good luck,