I usually don't leave this kind of comments, but I really can't read yellow text on dark red background for more than 20 seconds.
Oddly, I don't get the reader-mode option in Firefox for the site... one of these days I should probably figure out why that sometimes happens
It's an odd site design. Stories are loaded dynamically by script based on the URL fragment identifier; I'd imagine Reader Mode isn't geared toward that sort of thing.
I also wonder why they decided that hiding the scrollbar was a good idea.
That explains why the page was blank when I loaded it. No text without JS enabled.
For me it wasn't the color, but how smooshed the post body is. I had to override the max-width and added some letter-spacing.
Save to Instapaper and read on Kobo ;-)