A simple solution is to not use pure black/white for backgrounds (or text) - a ten percent shift can make a huge difference whilst still looking close enough to black/white for style purposes.
Browsers used to make it a simple option to toggle user styles only, which allowed people to be comfortable, but probably need an extension for that now and might not even work for a lot of the broken "modern" sites that infest the web.
Select all and copy-paste is usually still an option.
(p.s the actual worst people are those that require JavaScript to view content, and there's an ever growing amount of those arseholes.)