take regular tile, for example black or dark blue, mix epoxy-resin with glitter, and pour it on the tile (not after it's already tiled and grout)
- take regular tile, or maybe have just a square of epoxy-resin, take aluminum foil, crumple it up, straighten it again, then put it in the resin
- instead of aluminum foil, use those copper/tin foils that you press over a raised image to make shapes
- use copies of children's drawings on un-lined paper
- or any image at all