I just fixed this and pushed it up. Download again...
This makes your dark terminal background, that became light thanks to Darkroom mode, dark again.
It's a little bothersome to invert colors every time, but I guess I'm settling on this for now. I use powerline in tmux and vim, and there doesn't seem to be a quick way to configure it with light-background colors (and changing terminal color scheme doesn't affect its looks).
[0] Inverting colors is toggled with ^⎇⌘+8 by default. You may need to enable this shortcut in keyboard preferences.