What turned out to be fun and enlightening this time was that I drew all the white lines with a big tipped oil pen first (wanted a color that would show up on the dark rock) and later decided they would pop better if they were outlined in black and it worked. So, I guess you could say I learned something (perhaps).
Someone asked about protection: I spray my rocks with Krylon Fusion for Plastic with UV inhibitors, available at most hardware stores. The rocks have held up good outside in the sun and rain this Winter here in Lake Havasu. If they last a long time, great, if they last a short time, great. I consider them ephemeral (Yay Andy Goldsworthy) and will give them back to nature if they don't get claimed by some humans along the way.