There is a selectable marble design which has geometric shapes inside the marbles but the shapes ROTATE. It would be better if they remained stationary. The red marbles have a nearly-circular shape inside them and the green marbles have squares inside them. Pink marbles have triangles.
I'm going to try to hunt down an existing shot of these shape-containing marbles and if I can't find one I'll take a picture myself and post it.
OK, the quality is crappy but here's a shot on gamespot. The player on the right side is using the marbles with the shapes in them. Note how some of the green balls have the square shape rotated on-edge so you can't tell for sure what the shape is. The shapes rotate continuously so it doesn't take too long for them to be face-on again.