Questions about mixing custom colors

I found out some time ago that Risolve has a custom green hue they mix in-house. I was wondering if you have any experience and tips for doing this. Not the process of putting ink into the tubes but the compatibility of the "ingredients," I suppose. Do the components have to be from existing Riso manufactured colors only? Are they all compatible for mixing with each other? Can you mix in powder or liquid pigments into their ink?