I think you would need to bake the Modo replicator into individual meshes (if this is even possible) to do this.So if there is no way to control color independantly on a scatter node, can we take it the other way, treat the replicator as render time with an option like don't render as instance and make the plugin create real copy, and get the color automaticaly from the shader Inputs node ?
The Octane plugin converts Modo Replicators to Octane Scatter nodes, and that is pretty deeply ingrained in the plugin, and whilst in theory it could be changed, it would be a huge amount of work, and not something I think would be justified by the benefits that users would get.
Paul