better starting with a positive or negative image to produce color
separation
images for something like, say, gum bichromate? >>
Do you mean you are going to do the manual color separtion? If you need good
color reproduction, it is going to be very tedious because you will need
color correction masks, highlight mask, etc.
But if color accuracy is not a big concern, you can get by with just red,
green, and blue separation. Whether starting with a positive or negative is
better depends on whether you need negatives or positives for your
printmaking process. You can save one step if you use the right original, but
in any event, you can always make the extra step if needed.