I have just published my custom Node-RED dark theme. It's inspired by Ethan Schoonover's classic solarized dark color theme with the main difference of a dark grey background instead of a dark blue one.
It's installed in a similar manner as the popular Midnight theme and is infact hosted under the same GitHub organization. Installation instructions can be found at the repo: https://github.com/node-red-contrib-themes/solarized-dark-grey
A big thank you to @mbonani for regular reminders to complete and publish the theme, and also for letting me use @node-red-contrib-themes/midnight-red documentation template! Without his help it could have taken another 6 months for me to get this done.
NB: The theme also customizes node colors (as can be seen on the screenshot). This might be considered somewhat controversial. Custom node colors can be left out by leaving out
settings.js. Personally I feel the muted colors do not go well with the solarized palette....