Hello India,
I would like to help you out a bit with my own experience.
First of all, what camera do you use? I seriously recommend using a digital SLR, that is a professional interchangeable lens camera, and you can do away with a used one, with the most basic lens it comes with.
Here are my tips for you assessing each issue you mention:
– Distortion: When you get the DSLR, you’re best images will come out when walking a fews steps back and zooming in on the photo, that is because that focal length (longer) will distort the straight edges a lot less. Imagine taking the photos up close with a fish-eye lens, that will seriously distort them. To an extent, that is what happens when you are not far and zoomed in.
– Background: if you usually print on white paper, then you would want something to contrast it with. Like you mention a black background will draw from the colors of your prints because it will confuse the camera on what to expose for: background or foreground. White or black. Why not gray? That’s what the camera is calibrated to expose for, an 18% gray, now, you don’t need to use a gray background, but how about wood? it will be close to a neutral gray. I usually take my photos on the feed table of my press, and the crisp prints contrast nicely with the worn out wood used as background.
Staying true to the color: This will possibly be the hardest thing to get, because even if you go into Photoshop and eye-match the photo to your print, it will look different because the computer represents colors as emitted light, and not reflected like like a print. Even a print will look different under different light sources, so your best bet is to match it to your print to the best of your ability, even if it means altering individual hues in photoshop, and then be done with it.
– Prints on vellum or translucent paper: I have never been in this situation. So I’m sorry I’ll have to skip this one.
It works most of the time to photograph the stack, and one of the prints positioned off the stack.
Natural light is all I use, and I try to position prints so they receive the light perpendicular to the paper, which really makes the impression pop out.
Best of lucks!
Enrique