One problem that I foresee is getting the right color. When coloring a positive print what you see is what you get. When dealing with a negative finding the right complimentary color is more difficult. For example, while you may get a green is that just the shade of green you want.
i didn't think about that jerry
maybe tonight after i watch another few walking dead episodes
i will wake up in the middle of the night and shout " eureka ! "
but this will give me something to gnaw on ..