http://www.marinedepot.com/D_D_AquaScape_Aquarium_Epoxy_4oz_Reef_Glue_Epoxy_Putty_for_Saltwater_Aquariums-D_D_The_Aquarium_Solution-RW2111-FIMTEP-vi.html
They make a purple color "Coralline" I believe its called. Unless you want cement grey, I'd get the purple.
This stuff works great for...