I have nothing to add to the above but am chiming in with a question.
I have photographed my wife's art work for her web site and promotional materials but never for reproduction, e.g. producing prints for sale. Web sites and sales brochures are a less demanding output, it seems to me. If you get the colours close, that's as good as you need. Since they're not the final product, they just need to be good enough to attract attention.
Being able to produce prints for sale is a different and more complex task, it seems to me. I'd hate to think of the back and forth with the printing houses to get the colours right (or close). But do you approach the initial photo-taking differently in that case? (I don't photograph for a living, btw.)