I don't think that the corns would "like" it, as they are generally forest dwellers. The forest floor tends to be moister and more soft than gravel. And if your cornsare burrowers like mine are, gravel will be rough on their noses if they attempt to dig.
I have seen dealers at shows have their animals on black fish gravel to better show of the colors of the animals. It may work, just be careful during feeding time, you may want to serve their food on a plate.