Nikon D6 Reference Manual page 297

D
Time Limit (Live View)
Direct measurement mode will end if no operations are performed in the
time selected for Custom Setting c4 [Monitor off delay] > [Live view].
D
Measuring White Balance (Live View)
Preset manual white balance cannot be measured when [Multiple
exposure] is active or an option other than [None] is selected for [Photo
live view display WB] ( 0 848).
A
Touch Controls
In direct measurement mode, you can position the target ( U ) and
measure white balance by tapping the desired area in the display.
Achieving Natural Colors with Different Light Sources (White Balance)
245