Proofing through scanning is an interesting idea. I could imagine someone developing a complex process of proofing, measuring and adjusting pigment in order to dial in faithful color reproduction. But then I'm reminded of how compelling hand-colored photographs oftentimes are (think Curt Teich postcards as well as individually handwrought examples). Perhaps this quality has less to do with accurate color representation and more to do with large swaths of the photograph being covered by even-hued shades of color, lending a dreamy quality to what might otherwise be a very pedestrian view.

I think you should just go for it and use trial and error. I look forward to seeing the results!