Sometimes more than just two paint layers I think?!
There is/was Duratrans RA4 material which could perhaps be used to overlay a paper print (even the Ultra Endura pearlescents), or even some way of stripping the RC emulsion from the base? - but that sounds much less practical, especially for accurate registration.
Within one sheet of RA4 paper we can't selectively develop the emulsion-layers I think, though something similar was done in Kodachrome with the different couplers ??
I was looking at gum-bichromate tri-colour as an idea recently, but it seemed very very difficult to master in any predictable sort of way.