To make the marbled stones, take 1/2 of the fondant and put into a separate bowl or container. Add a coupe drops of grey food coloring and knead until fondant is completely covered. Grab a pinch of fondant from each white and grey and place one on top of the other. Twist them around each other, pull stretching them longer and fold. Do this a couple times creating a swirl effect. Repeat with remaining fondant. Shape into various sizes and shapes.