I ran across an old color photography technique called photochrom and I'd love to figure out a way to emulate it. My first thought is to duplicate the image and make a monochrome version, then use a live procedural texture on the original to create a number of single, non-CMYK/RGB color overlays, but I'm not quite sure how to create the procedural texture to do that. Has anyone done something like this? Is there another approach I could experiment with?