Did I dream that? Or is Mojave supposed to be capable of supporting Night Shift on external displays? If so, might it stop working because of sleeping/waking and/or attaching/detaching the monitor?
Night Shift is working on external monitors in Mojave.
Sometimes Night Shift deactivates itself on the external display when you wake the system from sleep. (Maybe a Bug?)
Just reactivate it manually.
- If Night Shift is off, go to the Night Shift tab in System Preferences>Display and check the box labelled Turn on until tomorrow.
- If Night Shift is on, click on the Schedule menu in the Night shift tab and choose ‘Off.’
- Use the color temperature slider in the same window to control the degree to which colors change when Night Switch is turned on or off.