KOOL!!! Last!
I have used colored pencils as a medium on rocks...YES, rocks!!! for several years and have sold many of my creations on Ebay under the seller name, "Artrox."
Similar to Kool Aid, as a child in imoverished conditions in rural Appalachia, I used to save the white cardboard between the layers of shredded wheat and draw on them!
Patty