Canon EOC-1DX Instruction Manual page 628

Displaying an Area Beyond the Set Range as a Warning Indicator (Highlight/Shadow Warning)
You can set up a warning indicator in both the highlighted part and the
shaded part, which is effective for checking the light and dark areas and
preventing excessive adjustment of an image. Where the area on the
image has exceeded that set range, you can display the highlighted part
in red and the shaded part in blue.
Select the [Digital Photo Professional] menu 
1
[Preferences].
2
Select the [View settings] tab sheet.
3 Enter the warning value for [Highlight] and [Shadow].
4 Click the [OK] button to close the window.
5 Display the edit window.
Select the [View] menu  [Highlight]. Similarly, select
6
[Shadow].
On the opened image, if there is an area that exceeds the value

entered in step 3, the highlighted part of that area is displayed in
red and the shaded part is displayed in blue.
You can also display the warning with the same operation in the edit
image window.
Introduction
Contents at
a Glance
1
Basic
Operation
2
Advanced
Operation
Advanced 3
Image Editing
and Printing
Processing 4
Large Numbers
of Images
Editing
5
JPEG/TIFF
Images
Reference
Index
55