Nikon D6 Reference Manual page 884

d10: Peaking Highlights
When focus peaking is enabled in manual focus mode, objects
that are in focus are indicated by colored outlines in the display.
You can choose the color.
Option
[Peaking
level]
[Peaking
highlight
color]
d11: Framing Grid Display
Choose whether to display a grid for reference when framing
shots.
832 A Custom Settings: Fine-Tuning Camera Settings
G button U A Custom Settings menu
Choose from [3 (high sensitivity)], [2 (standard)], [1
(low sensitivity)], and [Off]. The higher the value, the
greater the depth that will be shown as being in focus.
Choose a peaking highlight color from [Red], [Yellow],
[Blue], and [White].
G button U A Custom Settings menu
Description