Beryl is a color theme planned with a dark background in mind. Screenshots and details here:
Something I didn’t say in the README is that as long as your terminal uses standard xterm colors 17 to 256, the theme shoud look the same inside or outside tmux, and this, without needing to recompile the terminfo tmux database.
Also, I should (and will) file a bug report to Debian about Kakoune crashing when wide chars overlap a column highlighter.
Edit: added a screenshot with syntax highlighting for Bash.