It is really up to what you like. I have seen some done with all different fabrics and the center piece the same on each-very pretty. The only one I have made like this I used two different colors for the backround blocks and made the center pieces out of a third fabric. Then I had a really hard time deciding the layout once I got all the blocks done. I layed them on the floor and kept changing the layout of the blocks until I finally found one I liked the best don't stress too much. This is your quilt, do it whichever way you like the best.
Kat