I got curious and started styling a dark theme for the forums. Here's a draft of what I have so far:
https://imgur.com/Os0PTB3
One annoying thing is with Greasemonkey is that there is a delay between the style tag injection into the head, so when switching between pages you see a glimpse of the default white/blue theme before the custom theme takes over. I'll continue to mess around with my options on that.
If anyone is interested in this theme drop me a PM.