Part of macOS
corebrightnessdDisplay
○ Leave it
Manages brightness, colour and connected displays.
What it is
Handles brightness, True Tone, Night Shift and display colour.
If you stop it
macOS starts it again straight away. Leave it.
The verdict
○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.
In Activity Monitor
corebrightnessddisplaypolicydcolorsyncdcolorsync.displayservicescolorsync.useragentMirrorDisplays
From Procession’s guide, in the words the app shows.