I think most manufacturers use their own proprietary paint/dye to color their rock.
"Real Reef’s beautiful shades of Purple, Pink and Red come from a water based non-toxic natural pigment. These proprietary pigments are injected and applied through several techniques and processes. Every piece of Real Reef is hand made by our Artisans here at our U.S. facility with pride and creativity."
I don't think there is an off-the-shelf solution for you. It would be great if someone could invent it though, I'm sure it'll sell well!