I made the texturing work properly. Just look at this beautiful red sandstone.
Afterward, I added the support for multiple rock types. It is not working nearly as well as this screenshot might lead you to believe. I think I should have stuck with red sandstone, rather than this yellow type. Also, the limestone is looking very blue due to the depth cue. I should fix that.
I am still deciding between using natural stone colors, classifying stone colors, or abstract stone colors.