This might be where digital technology can come to the rescue.
I assume you are going to be working on some kind of light table. Yes?
Why not set up a digicam on a copy stand over your light table and take periodic pictures of your work in progress?
You could run them through Photoshop and reverse the colors to check how well you are doing.
The caveat is that your camera, your application software and your display will all have to be properly color calibrated so that you can see the colors as they closely approximate the way they will come out in the end.