Talk about difficult things to print: Scott Elliot of My SD300 3D Printer has been working on designs for marbles. Sure, one could easily print a sphere and call it a marble, but that's just too easy. Scott is designing a two-piece snap-together model with embedded colors and a twisty design.
As you might imagine, his approach is not really feasible on non-sheet-fed 3D printers. He simply inserts colored sheets into the feed hopper at the appropriate position to get the colors to look like a marble. However, we're wondering if colored marble designs are feasible with alternative techniques for other types of 3D printers?