When I asked the body shop about clay barring, they recommended the truck be buffed immediately afterwards. They said it will undoubtedly scratch the clear...but thats on black.
I'm gonna do mine next week while its in the body shop...kill two birds with one stone.
make sure to clean the car good to avoid as much scratching. I wash with dawn dish soap, clay bar, polish and finally apply a coat of wax.
I highly reccomend you do not use water or dish soap instead of the provide detailing spray. Water and dish are not lubericates. So you cause more scratchs then if you the correct product.