Mac OS Mojave introduces both a pretty dark mode and a way to trigger Automator scripts right from the Touch Bar. The two go together nicely:

1. Open Automator and create a “Quick Action”. This should receive “no input” and have a single “Run AppleScript” action with the following content:

tell application "System Events"
  tell appearance preferences
    set dark mode to not dark mode
  end tell
end tell

1. Save it, which will then land in your ~/Library/Services folder.
2. In your System Preferences > Keyboard > “Customise Touch Bar…”, drag the “Quick Actions” to your Touch Bar.

And – bam! – two taps on the Touch Bar, and you toggle between light and dark.

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I also tried (desperately) to switch the accent colour at the same time, but to no avail. The script below shows that there’s highlight color: orange, but I couldn’t get this to work. I’d appreciate any help from AppleScript pros.

tell application "System Events"
  tell appearance preferences
    get properties
    set highlight color to orange -- does nothing visually, though it does change that property :(
  end tell
end tell