I coat the newly cut piece with shellac, let it dry, mask off things that are a differing color than what I am currently working with and apply my color to the cut areas. Mask off the newly colored areas and expose the areas that are to get a differing color and apply that one then sand the surface.
most spray paints are soluble with lacquer thinner or mineral spirits and shellac does not react to these since its alcohol based. Here is what I came up with. 