Nikon Z9 Mirrorless Camera - Manual (Page 608)

608 A Custom Settings: Fine-Tuning Camera Settings
AF-C In-Focus Display
Choose whether the focus point changes color when the subject is in
focus in focus mode
AF-C .
Option Description
[ ON ]
The focus point is displayed in green when the camera judges
that the subject is in focus.
[ OFF ]
The active focus point is displayed in red or yellow at all times,
whether or not the camera is in focus.